Rigid structure UHMWPE UD and composite and the process of making

ABSTRACT

Fabrication of ballistic resistant fibrous composites having improved ballistic resistance properties. More particularly, ballistic resistant fibrous composites having enhanced flexural properties, which correlates to low composite backface signature. The composites are useful for the production of hard armor articles, including helmet armor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.13/594,747, filed Aug. 24, 2012, now U.S. Pat. No. 9,023,451, whichclaims the benefit of U.S. Provisional Application Ser. No. 61/531,302,filed on Sep. 6, 2011, the disclosures of which are incorporated byreference herein in their entireties.

BACKGROUND

Technical Field

The disclosure pertains to ballistic resistant fibrous composites havingenhanced flexural properties while maintaining superior ballisticpenetration resistance properties. The enhanced flexural propertiescorrelate to low composite backface signature and thus the compositesare particularly useful for the production of hard armor articles,including helmets meeting current National Institute of Justice (NIJ)backface signature requirements.

Description of the Related Art

Ballistic resistant articles fabricated from composites comprising highstrength synthetic fibers are well known. Articles such as bulletresistant vests, helmets, vehicle panels and structural members ofmilitary equipment are typically made from fabrics comprising highstrength fibers such as SPECTRA® polyethylene fibers or Kevlar® aramidfibers. For many applications, such as vests or parts of vests, thefibers may be used in a woven or knitted fabric. For other applications,the fibers may be encapsulated or embedded in a polymeric matrixmaterial and formed into non-woven fabrics. For example, U.S. Pat. Nos.4,403,012, 4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402,4,748,064, 5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, all ofwhich are incorporated herein by reference, describe ballistic resistantcomposites which include high strength fibers made from materials suchas extended chain ultra-high molecular weight polyethylene (“UHMW PE”).Ballistic resistant composites fabricated from such high strengthsynthetic fibers exhibit varying degrees of resistance to penetration byhigh speed impact from projectiles such as bullets, shells, shrapnel andthe like, as well as varying degrees of backface signature resultingfrom the same projectile impact.

It is known that each type of high strength fiber has its own uniquecharacteristics and properties. In this regard, one definingcharacteristic of a fiber is the ability of the fiber to bond with oradhere with surface coatings, such as resin coatings. For example,ultra-high molecular weight polyethylene fibers are relatively inert,while aramid fibers have a high-energy surface containing polarfunctional groups. Accordingly, resins generally exhibit a strongeraffinity aramid fibers compared to the inert UHMW PE fibers.Nevertheless, it is also generally known that synthetic fibers arenaturally prone to static build-up and thus typically require theapplication of a fiber surface finish in order to facilitate furtherprocessing into useful composites. Fiber finishes are employed to reducestatic build-up, and in the case of untwisted and unentangled fibers, toaid in maintaining fiber cohesiveness. Finishes also lubricate thesurface of the fiber, protecting the fiber from the equipment andprotecting the equipment from the fiber. The art teaches many types offiber surface finishes for use in various industries. See, for example,U.S. Pat. Nos. 5,275,625, 5,443,896, 5,478,648, 5,520,705, 5,674,615,6,365,065, 6,426,142, 6,712,988, 6,770,231, 6,908,579 and 7,021,349,which teach spin finish compositions for spun fibers.

However, typical fiber surface finishes are not universally desirable.One notable reason is because a fiber surface finish can interfere withthe interfacial adhesion or bonding of polymeric binder materials onfiber surfaces, including aramid fiber surfaces. Strong adhesion ofpolymeric binder materials is important in the manufacture of ballisticresistant fabrics, especially non-woven composites such as non-wovenSPECTRA SHIELD® composites produced by Honeywell International Inc. ofMorristown, N.J. Insufficient adhesion of polymeric binder materials onthe fiber surfaces may reduce fiber-fiber bond strength and fiber-binderbond strength and thereby cause united fibers to disengage from eachother and/or cause the binder to delaminate from the fiber surfaces. Asimilar adherence problem is also recognized when attempting to applyprotective polymeric compositions onto woven fabrics. This detrimentallyaffects the ballistic resistance properties (anti-ballistic performance)of such composites and can result in catastrophic product failure.

The anti-ballistic performance of composite armor can be characterizedin different ways. One common characterization is the V₅₀ velocity,which is the experimentally derived, statistically calculated impactvelocity at which a projectile is expected to completely penetrate armor50% of the time and be completely stopped by the armor 50% of the time.For composites of equal areal density (i.e. the weight of the compositepanel divided by the surface area) the higher the V₅₀ the better thepenetration resistance of the composite. However, even whenanti-ballistic armor is sufficient to prevent the penetration of aprojectile, the impact of the projectile on the armor may also causesignificant non-penetrating, blunt trauma (“trauma”) injuries.Accordingly, another important measure of anti-ballistic performance isarmor backface signature. Backface signature (“BFS”), also known in theart as backface deformation or trauma signature, is the measure of thedepth of deflection of body armor due to a bullet impact. When a bulletis stopped by composite armor, potentially resulting blunt traumainjuries may be as deadly to an individual as if the bullet hadpenetrated the armor and entered the body. This is especiallyconsequential in the context of helmet armor, where the transientprotrusion caused by a stopped bullet can still cross the plane of thewearer's skull and cause debilitating or fatal brain damage.

It is known that the V₅₀ ballistic performance of a composite isdirectly related to the strength of the constituent fibers of thecomposite. Increases in fiber strength properties such as tenacityand/or tensile modulus are known to correlate with an increase in V₅₀velocity. However, a corresponding improvement of backface signaturereduction with increased fiber strength properties has not beensimilarly recognized. Accordingly, there is a need in the art for amethod to produce ballistic resistant composites having both superiorV₅₀ ballistic performance as well as low backface signature. Thedisclosure provides a solution to this need.

It has been unexpectedly found that there is a direct correlationbetween backface signature and the tendency of the component fibers of aballistic resistant composite to delaminate from each other and/ordelaminate from fiber surface coatings as a result of a projectileimpact. By improving the bond between a fiber surface and a fibersurface coating, the fiber-fiber disengagement and/or fiber-coatingdelamination effect are reduced, thereby increasing friction on thefibers and increasing projectile engagement with the fibers.Accordingly, the composite structural properties are improved and theenergy of a projectile impact is dissipated in a manner that reduces thecomposite backface deformation.

The disclosure addresses this need in the art by processing the fibersto improve the bond between a fiber surface and a fiber surface coatingprior to uniting the fibers as non-woven fiber layers or fabrics, orprior to weaving fibers into woven fabrics, and prior to coating thefibers with select polymers, as well as prior to merging multiple fiberlayers into a multi-ply or multi-layer composite. It has been found thatfibrous composites formed from such treated fibers have a stress atyield that is greater than the stress at yield of a comparable fibrouscomposite that has not been similarly treated. Particularly, the fibersare processed to remove at least a portion of the fiber surface finishto expose at least a portion of the fiber surface, thereby allowing asubsequently applied polymer to bond directly with the fiber surfacesuch that the polymer is predominantly in direct contact with the fibersurface rather than predominantly atop the finish. A variety of otherfiber treatments may also be conducted to further enhance the ability ofa subsequently applied material to adsorb to, adhere to or bond to thefiber surface. The higher stress at yield reflects increased fiber-fiberbonding within a single fiber ply, increased ply-ply bonding within asingle multi-ply fabric or multi-ply fiber layer, and correlates toimproved composite structural properties as well as improved compositebackface signature.

SUMMARY OF THE DISCLOSURE

The disclosure provides a fibrous composite comprising a plurality ofadjoined fiber layers, each fiber layer comprising fibers havingsurfaces that are at least partially covered with a polymeric material,wherein said fibers are predominantly free of a fiber surface finishsuch that said polymeric material is predominantly in direct contactwith the fiber surfaces; said fibrous composite having a stress at yieldthat is greater than the stress at yield of a comparable fibrouscomposite having fiber surfaces that are predominantly covered with afiber surface finish wherein such a fiber surface finish is between thefiber surfaces and the polymeric material.

The disclosure also provides a method of forming a fibrous compositecomprising at least two adjoined fiber layers, each fiber layercomprising fibers having surfaces that are at least partially coveredwith a polymeric material, wherein said fibers are predominantly free ofa fiber surface finish such that said polymeric material ispredominantly in direct contact with the fiber surfaces; said compositehaving a stress at yield of at least 7.50 ksi (˜51.71 MPa) as measuredby ASTM D790 for a composite having an areal density of about 1.5 lb/ft²(7.32 kg/m²) or less, the method comprising providing a plurality ofpolymeric fibers having surfaces that are predominantly free of a fibersurface finish; optionally treating the fiber surfaces to enhance thesurface adsorbability, bonding or adhesion of a subsequently appliedpolymeric material to the fiber surfaces; applying a polymeric materialonto at least a portion of said fibers, thereby adsorbing, bonding oradhering the polymeric material on or to the fiber surfaces; producing aplurality of fiber plies from said fibers either before or afterapplying said polymeric material to said fibers; and consolidating saidplurality of fiber plies to produce a fibrous composite.

The disclosure further provides a composite comprising a consolidatedplurality of fiber layers, each of said fiber layers comprising aplurality of fibers having a tenacity of about 7 g/denier or more and atensile modulus of about 150 g/denier or more, wherein each fiber layeris at least partially impregnated with a polymeric binder material, thepolymeric binder material substantially coating the fibers, and saidpolymeric binder material comprising from about 7% to about 20% byweight of each fiber layer; said panel having a stress at yield of atleast 7.50 ksi (˜51.71 MPa) as measured by ASTM D790, a composite arealdensity of about 1.5 lb/ft² (7.32 kg/m²) or less and a V₅₀ value of atleast about 1750 feet/sec (fps) (533.40 m/s) against a 9 mm projectilein accordance with Department of Defense Test Method StandardMIL-STD-662F.

DETAILED DESCRIPTION

Backface signature is a measure of the depth of deflection of eithersoft or hard armor into a backing material or into a user body due to aprojectile impact. More specifically, BFS, also known in the art as“backface deformation”, “trauma signature” or “blunt force trauma”, is ameasure of how much impact a projectile leaves under the armor once thearmor stops the projectile from penetrating, indicating the potentialblunt trauma experienced by the body underneath the armor. The standardmethod for measuring BFS of soft armor is outlined by NIJ Standard0101.04, Type IIIA, which identifies a method of transferring thephysical deformation of a composite resulting from a non-penetratingprojectile impact into a deformable clay backing material held in anopen face, box-like fixture. Per the NIJ standard, the armor beingtested is secured directly to a front surface of the clay backing andany deformation of the clay resulting from standardized projectilefiring conditions is identified and measured. Other methods may be usedto measure BFS. The NIJ standard is conventionally used at the presenttime to evaluate soft armor composites intended for military use.

The terms “backface signature”, “backface deformation”, “traumasignature” and “blunt force trauma” have the same meaning in the art andare used interchangeably herein. For the purposes of the invention,articles that have superior ballistic penetration resistance describethose which exhibit excellent properties against deformable projectiles,such as bullets, and against penetration of fragments, such as shrapnel.A “fiber layer” as used herein may comprise a single-ply ofunidirectionally oriented fibers, a plurality of non-consolidated pliesof unidirectionally oriented fibers, a plurality of consolidated pliesof unidirectionally oriented fibers, a woven fabric, a plurality ofconsolidated woven fabrics, or any other fabric structure that has beenformed from a plurality of fibers, including felts, mats and otherstructures, such as those comprising randomly oriented fibers. A “layer”describes a generally planar arrangement. Each fiber layer will haveboth an outer top surface and an outer bottom surface. A “single-ply” ofunidirectionally oriented fibers comprises an arrangement ofnon-overlapping fibers that are aligned in a unidirectional,substantially parallel array. This type of fiber arrangement is alsoknown in the art as a “unitape”, “unidirectional tape”, “UD” or “UDT.”As used herein, an “array” describes an orderly arrangement of fibers oryarns, which is exclusive of woven fabrics, and a “parallel array”describes an orderly parallel arrangement of fibers or yarns. The term“oriented” as used in the context of “oriented fibers” refers to thealignment of the fibers as opposed to stretching of the fibers. The term“fabric” describes structures that may include one or more fiber plies,with or without molding or consolidation of the plies. For example, awoven fabric or felt may comprise a single fiber ply. A non-woven fabricformed from unidirectional fibers typically comprises a plurality offiber plies stacked on each other and consolidated. When used herein, a“single-layer” structure refers to any monolithic fibrous structurecomposed of one or more individual plies or individual layers that havebeen merged, i.e. consolidated by low pressure lamination or by highpressure molding, into a single unitary structure together with apolymeric binder material. By “consolidating” it is meant that thepolymeric binder material together with each fiber ply is combined intoa single unitary layer. Consolidation can occur via drying, cooling,heating, pressure or a combination thereof. Heat and/or pressure may notbe necessary, as the fibers or fabric layers may just be glued together,as is the case in a wet lamination process. The term “composite” refersto combinations of fibers with at least one polymeric binder material. A“complex composite” as used herein refers to a consolidated combinationof a plurality of fiber layers. As described herein, “non-woven” fabricsinclude all fabric structures that are not formed by weaving. Forexample, non-woven fabrics may comprise a plurality of unitapes that areat least partially coated with a polymeric binder material,stacked/overlapped and consolidated into a single-layer, monolithicelement, as well as a felt or mat comprising non-parallel, randomlyoriented fibers that are preferably coated with a polymeric bindercomposition.

For the purposes of the present invention, a “fiber” is an elongate bodythe length dimension of which is much greater than the transversedimensions of width and thickness. The cross-sections of fibers for usein this invention may vary widely, and they may be circular, flat oroblong in cross-section. Thus the term “fiber” includes filaments,ribbons, strips and the like having regular or irregular cross-section,but it is preferred that the fibers have a substantially circularcross-section. As used herein, the term “yarn” is defined as a singlestrand consisting of multiple fibers. A single fiber may be formed fromjust one filament or from multiple filaments. A fiber formed from justone filament is referred to herein as either a “single-filament” fiberor a “monofilament” fiber, and a fiber formed from a plurality offilaments is referred to herein as a “multifilament” fiber.

In the context of the present invention, the term “stress at yield” of acomposite is used herein as a measure of the flexural strength of acomposite and refers to the amount of flexural stress that may beapplied to a composite before the component layers or plies of thecomposite begin to delaminate or detach from each other. Most typically,this delamination is exhibited by a failure of the resin-fiber bond,thereby causing some or all of the fibers within a ply/layer to separatefrom each other, or causing entire plies/layers within a composite toseparate from each other, as opposed to a failure or breakage of thecomponent fibers. Accordingly, resin-fiber bond enhancing treatments aredesirable for increasing the stress at yield.

A preferred method for measuring the stress at yield of a composite isknown as a three-point bend test, such as the three-point bend testmethod of ASTM standard D790 or of ISO method 178. A three-point bendtest, also known as a three-point flexural test, measures the forcerequired to bend a composite specimen under three-point loadingconditions. In a typical process, a beam-shaped or bar-shaped specimenis placed evenly on supports at opposite ends of the beam/bar with anopen span of a specified distance between the supports. A load isapplied at a specified rate to the center of the specimen, such as witha loading nose, causing the specimen to bend. The load is applied for aspecified time. According to the method of ASTM D790, the load isapplied until the specimen reaches 5% deflection or until the specimenbreaks. According to the method of ISO 178, the load is applied untilthe specimen breaks and the stress at 3.5% deflection is reported. Forthe purposes of this invention, a load is applied at least until atleast partial delamination of at least a part of the composite occurs.Testing may be conducted using any suitable three-point bend testingmachine or universal testing machine with a three-point fixture may beused, including the 2810 Series Bend/Flexure Fixture devicescommercially available from Instron Corporation of Norwood, Mass.

The three-point bend test is preferred for its simplicity. However,because the results of the testing method are sensitive to factors suchas size of the tested specimen, geometry of the specimen, span betweenthe end supports, strain rate and ambient temperature, it is preferredand ideal that all factors are kept constant during comparative testingwith the type of composite specimen being tested or fiber treatments asthe only test variable.

When measuring the flexural properties such as stress at yield of acomposite of the invention, the composites as tested should comprise orconsist of a plurality of adjoined fiber layers/plies, each fiber layercomprising fibers having surfaces that are at least partially coveredwith a polymeric material. As used herein, adjoined fiber layers mayinclude adjoined unitapes and/or adjoined woven fabrics, and the fiberlayers/plies may be adjoined by any conventional technique in the art.Adjoined unitapes are typically arranged in a conventional cross-plied0°/90° orientation to maximize ballistic penetration resistance (e.g. asdetermined by standardized V₅₀ testing), although this orientation isnot mandatory and not necessarily optimal for minimizing backfacedeformation of a composite. Adjoined unitapes are consolidated using apolymeric binder material as described in greater detail below. Unlikenon-woven fabrics, woven fabrics do not require a polymeric bindermaterial to interconnect the component fibers to form a single fiberlayer. However, an adhesive or polymeric binder material is generallyneeded to consolidate or merge multiple woven fiber layers into amulti-layer fibrous composite. Accordingly, it is generally necessarythat some form of adhesive or polymeric binder material be present forma composite including at least some woven fabric layers in order to testthe stress at yield of the composite. In a preferred embodiment, wovenfabrics are pre-impregnated with a polymeric binder material priorconsolidation.

In all of the inventive examples illustrated below, three-point bendtesting was performed on composites comprising non-woven fiber layers,measuring flexural properties including displacement at yield, strain atyield, load at yield, stress at yield and energy to yield point. Eachcomposite was formed from a consolidated plurality of 2-ply non-wovenfiber layers comprised of a first ply oriented at 0° and a second plyoriented at 90°. Testing of each example was conducted at roomtemperature (appx. 70° F.-72° F.) unless specified otherwise, as per theconditions of ASTM D790. The temperature of testing is an importantfactor when testing materials incorporating thermoplastic polymersbecause higher temperatures tend to soften thermoplastic polymers,altering the flexural properties of the material.

The fibrous composites of the invention are distinguished from otherfibrous composites by their greater flexural properties, as measured forexample by the stress at yield of the composite, and a correspondinglysuperior backface signature performance against high velocity,non-penetrating projectiles. The improvement in the flexural propertiesof the fibrous composites of the invention is achieved by, at minimum,at least partially removing a pre-existing fiber surface finish from thefibers prior to processing the fibers into a fabric, wherein forming afabric includes the fabrication of woven fabric layers, non-woven fabriclayers or a non-woven fiber plies. The removal of fiber surface finishesprior to the formation of non-woven fabric layers or non-woven fiberplies, or prior to the weaving of woven fabrics, has not hereinbeforebeen known because the fiber surface finish is generally known as anecessary processing aid as described above. For example, in thefabrication of non-woven fabrics, a fiber surface finish is generallyrequired to reduce static build-up, prevent fiber tangling, lubricatethe fiber to allow it to slide over loom components, and improve fibercohesion during processing, including during fiber drawing steps.

While fiber surface finishes are typically needed during conventionalfabric processing, they generally do not contribute to the final fabricproperties. To the contrary, by covering fiber surfaces, the finishinterferes with the ability of the fiber surfaces to contact each other,and interferes with the ability of the fiber surfaces to directly adsorbsubsequently applied adsorbates, such as liquid or solid resins orpolymeric binder materials that are applied onto the fibers, positioningthe adsorbates on top of the finish rather than directly on the fibersurfaces. This is problematic. In the former situation, the finish actsas a lubricant on the fiber surfaces and thus reduces friction betweenadjacent fibers. In the latter situation, the finish preventssubsequently applied materials from bonding directly and strongly to thefiber surfaces, potentially preventing coatings from bonding to fibersaltogether, as well as risking delamination during a ballistic impact.To enhance fiber-fiber friction and to permit direct bonding of resinsor polymeric binder materials to the fiber surfaces, thereby increasingthe fiber-coating bond strength, it is necessary that the existing fibersurface finish be at least partially removed, and preferablysubstantially completely removed from all or some of the fiber surfacesof some or all of the component fibers forming a fibrous composite.

The at least partial removal of the fiber surface finish will preferablybegin once all fiber drawing/stretching steps have been completed. Thestep of washing the fibers or otherwise removing the fiber finish willremove enough of the fiber finish so that at least some of theunderlying fiber surface is exposed, although different removalconditions should be expected to remove different amounts of the finish.For example, factors such as the composition of the washing agent (e.g.water), mechanical attributes of the washing technique (e.g. the forceof the water contacting the fiber; agitation of a washing bath, etc.),will affect the amount of finish that is removed. For the purposesherein, minimal processing to achieve minimal removal of the fiberfinish will generally expose at least 10% of the fiber surface area.Preferably, the fiber surface finish is removed such that the fibers arepredominantly free of a fiber surface finish. As used herein, fibersthat are “predominantly free” of a fiber surface finish are fibers whichhave had at least 50% by weight of their finish removed, more preferablyat least about 75% by weight of their finish removed, more preferably atleast about 80% by weight of their finish removed. It is even morepreferred that the fibers are substantially free of a fiber surfacefinish. Fibers that are “substantially free” of a fiber finish arefibers which have had at least about 90% by weight of their finishremoved, and most preferably at least about 95% by weight of theirfinish removed, thereby exposing at least about 90% or at least about95% of the fiber surface area that was previously covered by the fibersurface finish. Most preferably, any residual finish will be present inan amount of less than or equal to about 0.5% by weight based on theweight of the fiber plus the weight of the finish, preferably less thanor equal to about 0.4% by weight, more preferably less than or equal toabout 0.3% by weight, more preferably less than or equal to about 0.2%by weight and most preferably less than or equal to about 0.1% by weightbased on the weight of the fiber plus the weight of the finish.

Depending on the surface tension of the fiber finish composition, afinish may exhibit a tendency to distribute itself over the fibersurface, even if a substantial amount of the finish is removed. Thus, afiber that is predominantly free of a fiber surface finish may stillhave a portion of its surface area covered by a very thin coating of thefiber finish. However, this remaining fiber finish will typically existas residual patches of finish rather than a continuous coating.Accordingly, a fiber having surfaces that are predominantly free of afiber surface finish preferably has its surface at least partiallyexposed and not covered by a fiber finish, where preferably less than50% of the fiber surface area is covered by a fiber surface finish. Thefibrous composites of the invention comprising fiber surfaces that arepredominantly free of a fiber finish are then coated with a polymericbinder material. Where removal of the fiber finish has resulted in lessthan 50% of the fiber surface area being covered by a fiber surfacefinish, the polymeric binder material will thereby be in direct contactwith greater than 50% of the fiber surface area.

As a result of such finish removal, fibrous composites of the inventionhave stress at yield that is greater than the stress at yield of acomparable fibrous composite having fibers that are predominantlycovered with a fiber surface finish, e.g. where a fiber surface finishis present between the fiber surfaces and the polymeric material ongreater than 50% of the fiber surface area.

Most preferably, the fiber surface finish is substantially completelyremoved from the fibers and the fiber surfaces are substantiallycompletely exposed. In this regard, a substantially complete removal ofthe fiber surface finish is the removal of at least about 95%, morepreferably at least about 97.5% and most preferably at least about 99.0%removal of the fiber surface finish, and whereby the fiber surface is atleast about 95% exposed, more preferably at least about 97.5% exposedand most preferably at least about 99.0% exposed. Ideally, 100% of thefiber surface finish is removed, thereby exposing 100% of the fibersurface area. Following removal of the fiber surface finish, it is alsopreferred that the fibers are cleared of any removed finish particlesprior to application of a polymeric binder material, resin or otheradsorbate onto the exposed fiber surfaces.

As used herein, a “comparable” fibrous composite is defined as acomposite (theoretical or real) which is identical or substantiallysimilar to a treated composite of the invention where the inventivecomposite has had at least a portion of the fiber surface finish removedto expose at least a portion of the fiber surface, optionally withadditional fiber treatments such as plasma treating or corona treating,and where a polymeric material is accordingly bonded directly to thefiber surface in areas where the finish has been removed. In thisregard, “substantially similar” refers to any minimal error experiencedwhen setting the constant factors. In other words, the comparablefibrous composite is a “control composite” to which a “treatedcomposite” of the invention is compared. Particularly, both the controlcomposite and treated composite of the invention will both be fabricatedfrom the same fiber type (same fiber chemistry, tenacity, modulus,etc.), comprise the same fiber layer structure (e.g. woven ornon-woven), comprise the same type of polymeric material (also referredto as a binder polymer, polymeric binder material or polymeric matrix)that is coated on the fibers, the same quantity of resin in thecomposite, the same number of fiber plies/layer, etc. Both the controlcomposite and treated composite will also be formed according to thesame consolidation/molding conditions. All factors except for the fibersurface treatments described herein are intended to be kept constant.These are all important considerations because data has shown, forexample, that BFS and flexural properties such as stress at yield aredependent to some extent on the type of resin used, just like BFS andflexural properties are dependent to some extent on the presence of afiber finish and on the surface treatments of the fiber. The datapresented herein supports this premise that a treated composite willexhibit improved BFS and flexural properties relative to an identical orsubstantially similar control composite, not necessarily relative toother composites having elements that are not kept constant. Asprocessing of the fibers to achieve minimal removal of the fiber finishwill generally expose at least about 10% of the fiber surface area, acomparable composite which has not been similarly washed or treated toremove at least a portion of the fiber finish will have less than 10% ofthe fiber surface area exposed, with zero percent surface exposure orsubstantially no fiber surface exposure.

As previously described, removal of the fiber surface finish enhancesfiber-fiber friction as well as the bond strength between the fiber anda subsequently applied coating. Increasing fiber-fiber friction andincreasing fiber-coating bond strength has been found to increaseprojectile engagement with the fibers, thereby improving the flexuralproperties of fibrous composites formed from said fibers, as well asimproving the ability of fibrous composites formed from said fibers tostop projectiles, and also reducing backface signature resulting from aprojectile impact. The improved fiber-coating bond strength also reducesthe amount of binder needed to adequately bind the fibers together. Thisreduction in binder quantity allows a greater number of fibers to beincluded in a fabric, which allows for potentially producing lighterballistic materials having improved strength. This also leads to furtherimproved stab resistance of the resulting fabric composites as well asan increased resistance of the composites against repeated impacts.

Any conventionally known method for removing fiber surface finishes isuseful within the context of the present invention, including bothmechanical and chemical techniques means. The necessary method isgenerally dependent on the composition of the finish. For example, inthe preferred embodiment of the invention, the fibers are coated with afinish that is capable of being washed off with only water. Typically, afiber finish will comprise a combination of one or more lubricants, oneor more non-ionic emulsifiers (surfactants), one or more anti-staticagents, one or more wetting and cohesive agents, and one or moreantimicrobial compounds. The finish formulations preferred herein can bewashed off with only water. Mechanical means may also be employedtogether with a chemical agent to improve the efficiency of the chemicalremoval. For example, the efficiency of finish removal using de-ionizedwater may be enhanced by manipulating the force, direction velocity,etc. of the water application process.

Most preferably, the fibers are washed and/or rinsed with water as afiber web, preferably using de-ionized water, with optional drying ofthe fibers after washing, without using any other chemicals. In otherembodiments where the finish is not water soluble, the finish may beremoved or washed off with, for example, an abrasive cleaner, chemicalcleaner or enzyme cleaner. For example, U.S. Pat. Nos. 5,573,850 and5,601,775, which are incorporated herein by reference, teach passingyarns through a bath containing a non-ionic surfactant (Hostapur® CX,commercially available from Clariant Corporation of Charlotte, N.C.),trisodium phosphate and sodium hydroxide, followed by rinsing thefibers. Other useful chemical agents non-exclusively include alcohols,such as methanol, ethanol and 2-propanol; aliphatic and aromatichydrocarbons such as cyclohexane and toluene; chlorinated solvents suchas di-chloromethane and tri-chloromethane. Washing the fibers will alsoremove any other surface contaminants, allowing for more intimatecontact between the fiber and resin or other coating material.

The preferred means used to clean the fibers with water is not intendedto be limiting except for the ability to substantially remove the fibersurface finish from the fibers. In a preferred method, removal of thefinish is accomplished by a process that comprises passing a fiber webthrough pressurized water nozzles to wash (or rinse) and/or physicallyremove the finish from the fibers. The fibers may optionally bepre-soaked in a water bath before passing the fibers through saidpressurized water nozzles, and/or soaked after passing the fibersthrough the pressurized water nozzles, and may also optionally be rinsedafter any of said optional soaking steps by passing the fibers throughadditional pressurized water nozzles. The washed/soaked/rinsed fibersare preferably also dried after washing/soaking/rinsing is completed.The equipment and means used for washing the fibers is not intended tobe limiting, except that it must be capable of washing individualmultifilament fibers/multifilament yarns rather than fabrics, i.e.before they are woven or formed into non-woven fiber layers or plies.

The removal of the fiber surface finish prior to fabric formation isespecially intended herein for the production of non-woven fabrics thatare formed by consolidating a plurality of fiber plies that comprise aplurality of unidirectionally aligned fibers. In a typical process forforming non-woven unidirectionally aligned fiber plies, fiber bundlesare supplied from a creel and led through guides and one or morespreader bars into a collimating comb, followed by coating the fiberswith a polymeric binder material. Alternately the fibers can be coatedbefore encountering the spreader bars, or they may be coated between twosets of spreader bars, one before and one after the coating section. Atypical fiber bundle (e.g. a yarn) will have from about 30 to about 2000individual filaments, each fiber typically including, but not limitedto, from about 120 to about 240 individual filaments. The spreader barsand collimating comb disperse and spread out the bundled fibers,reorganizing them side-by-side in a coplanar fashion. Ideal fiberspreading results in the individual fibers, or even individualfilaments, being positioned next to one another in a single fiber plane,forming a substantially unidirectional, parallel array of fibers with aminimal amount of fibers overlapping each other. Removing the fibersurface finish before or during this spreading step may enhance andaccelerate the spreading of the fibers into such a parallel array due tothe physical interaction of the cleaning agent (e.g. water) with whichthe fibers/filaments interact. Following fiber spreading andcollimating, the fibers of such a parallel array will typically containfrom about 3 to 12 fiber ends per inch (1.2 to 4.7 ends per cm),depending on the fiber thickness. Accordingly, removal of the fibersurface finish achieves a dual benefit of enhancing fiber spreading andimproves the bond strength of subsequently applied materials/adsorbateson the fiber surfaces.

While removal of the fiber surface finish alone achieves theaforementioned benefits, even greater results may be achieved byconducting bond enhancing treatments on the fiber surfaces after the atleast partial finish removal. In particular, it has been found thatbackface signature reduction is directly proportional to increases infiber-fiber friction and fiber-coating bond strength. Treating ormodifying the fiber surfaces with a bond enhancing treatment prior tofabric formation has been found to achieve even greater improvements incomposite backface signature reduction, particularly when the bondenhancing treatment is combined with washing the fibers to at leastpartially remove the fiber finish. This is particularly evident when anadsorbate such as a polymeric binder material or resin is applied ontothe fiber surfaces, such as a polymeric binder material or resin that isconventionally used for fabrication of non-woven fabrics, or which isapplied after weaving fabrics and at least partially removing a fibersurface finish. The stronger the bond of the adsorbate (e.g.polymer/resin) to the fiber surface, the greater the reduction inbackface signature. Accordingly, in the most preferred embodiments ofthe invention, after the at least partial removal of the fiber surfacefinish, but prior to fabric formation, it is particularly desired toconduct a treatment of the fiber surfaces under conditions effective toenhance the adsorbability/bonding of a subsequently applied adsorbate(e.g. polymer/resin) on the fiber surfaces. Removal of the fiber finishallows these additional processes to act directly on the surface of thefiber and not on the fiber surface finish or on surface contaminants.This is most desired because surface finishes tend to interfere withattempts to treat the surface of the fiber, acting as a barrier orcontaminant. Removal of the finish thus also improves the quality anduniformity of subsequent fiber surface treatments. The benefits offinish removal and such further treatments are cumulative, andimprovements in backface signature performance should increase with anincreased percentage of finish removal and with greater effectiveness ofthe treatments.

To this end, useful treatments or modifications include anything that iseffective to enhance the adsorbability of a subsequently appliedadsorbate on the fiber surfaces, where an adsorbate may be any solid,liquid or gas, including polymeric binder materials and resins, andwhere adsorption includes any form of bonding of the materials to thefiber surfaces. There are various means by which this may beaccomplished, including treatments that roughen the surface, addpolarity to the surface, oxidize the fiber surface or fiber surfacemoieties, increase the surface energy of the fiber, reduce the contactangle of the fiber, increase wettability of the fiber, modify thecrosslink density of the fiber surface, add a chemical functionality tothe fiber surface, ablate the surface, or any other means of improvingthe interaction between the bulk fiber and fiber surface coatings toimprove the anchorage of the coatings to fiber surfaces. This modifiedinteraction can easily be seen in improvements in BFS.

Suitable fiber surface treatments or surface modifications includeprocesses that may be known in the art, such as corona treating thefibers, plasma treating the fibers, plasma coating the fibers, directfluorination of the fiber surfaces with elemental fluorine, a chemicaltreatment such as chemical UV grafting, or a surface rougheningtreatment, such as chromic etching. Also suitable are treatments thatare yet undeveloped for large scale application that enhance the abilityof an adsorbate to adsorb on or any material to bond with the exposedand treated fiber surfaces following removal fiber surface finish butprior to fabric formation. Each of these exemplary processes, throughtheir action on the surface of the fiber, can be employed to modify,improve or reduce the interaction between the bulk fiber and subsequentcoating materials, depending on fiber chemistry. Any combination ofthese processes can be employed and these sub-processes can be placed indifferent sequences, although there may be some sequences that arepreferred over others depending on various factors, such as fiber typeor natural fiber surface properties. The various treatment steps of theinvention may be utilized as a recipe for manipulating the fibers inorder to place the composite within the desired range for flexuralproperties, e.g. stress at yield. If three point bend testing determinesthat a particular composite has a lower stress at yield than desired(e.g. less than 7.50 ksi), that is indicative that further fiber washingand/or further surface treatments (e.g. corona treatment, plasmatreatment, etc.) should be conducted to further increase the flexuralstrength so that the stress at yield to falls within the desired range.

The most preferred treatments are corona treatment of the fiber surfacesand plasma treatment of the fiber surfaces. Corona treatment is aprocess in which a fiber is passed through a corona discharge station,thereby passing the fiber web through a series of high voltage electricdischarges, which tend to act on the surface of the fiber web in avariety of ways, including pitting, roughing and introducing polarfunctional groups by way of partially oxidizing the surface of thefiber. Corona treatment typically oxidizes the fiber surface and/or addspolarity to the fiber surface. Corona treatment also acts by burningsmall pits or holes into the surface of the fiber. When the fibers areoxidizable, the extent of oxidation is dependent on factors such aspower, voltage and frequency of the corona treatment. Residence timewithin the corona discharge field is also a factor, and this can bemanipulated by corona treater design or by the line speed of theprocess. Suitable corona treatment units are available, for example,from Enercon Industries Corp., Menomonee Falls, Wis., from ShermanTreaters Ltd, Thame, Oxon., UK, or from Softal Corona & Plasma GmbH & Coof Hamburg, Germany.

In a preferred embodiment, the fibers are subjected to a coronatreatment of from about 2 Watts/ft²/MIN to about 100 Watts/ft²/MIN, morepreferably from about 20 Watts/ft²/MIN to about 50 Watts/ft²/MIN. Lowerenergy corona treatments from about 1 Watts/ft²/MIN to about 5Watts/ft²/MIN are also useful may be less effective. In addition toapplying a charge to the fiber surface, a corona treatment may roughenthe surface by pitting the surface of the fiber.

In a plasma treatment, the fibers, typically as a fiber web, are passedthrough an ionized atmosphere in a chamber that is filled with an inertor non-inert gas, such as oxygen, argon, helium, ammonia, or anotherappropriate inert or non-inert gas, including combinations of the abovegases, to thereby contact the fibers with an electric discharge. At thefiber surfaces, collisions of the surfaces with charged particles (ions)result in both the transfer of kinetic energy and the exchange ofelectrons, etc. In addition, collisions between the surfaces and freeradicals will result in similar chemical rearrangements. Bombardment ofthe fiber surface by ultraviolet light that is emitted by excited atomsand molecules relaxing to lower states also causes chemical changes tothe fiber substrate.

As a result of these interactions, the plasma treatment may modify boththe chemical structure of the fiber as well as the topography of thefiber surfaces. For example, like corona treatment, a plasma treatmentmay also add polarity to the fiber surface and/or oxidize fiber surfacemoieties. Plasma treatment may also serve to increase the surface energyof the fiber, reduce the contact angle, modify the crosslink density ofthe fiber surface, increase the melting point and the mass anchorage ofsubsequent coatings, and may add a chemical functionality to the fibersurface and potentially ablate the fiber surface. These effects arelikewise dependent on the fiber chemistry, and are also dependent on thetype of plasma employed.

The selection of gas is important for the desired surface treatmentbecause the chemical structure of the surface is modified differentlyusing different plasma gases. Such would be determined by one skilled inthe art. It is known, for example, that amine functionalities may beintroduced to a fiber surface using ammonia plasma, while carboxyl andhydroxyl groups may be introduced by using oxygen plasma. Accordingly,the reactive atmosphere may comprise one or more of argon, helium,oxygen, nitrogen, ammonia, and/or other gas known to be suitable forplasma treating of fabrics. The reactive atmosphere may comprise one ormore of these gases in atomic, ionic, molecular or free radical form.For example, in a preferred continuous process of the invention, anarray of fibers is passed through a controlled reactive atmosphere thatpreferably comprises argon atoms, oxygen molecules, argon ions, oxygenions, oxygen free radicals, as well as other trace species. In apreferred embodiment, the reactive atmosphere comprises both argon andoxygen at concentrations of from about 90% to about 95% argon and fromabout 5% to about 10% oxygen, with 90/10 or 95/5 concentrations ofargon/oxygen being preferred. In another preferred embodiment, thereactive atmosphere comprises both helium and oxygen at concentrationsof from about 90% to about 95% helium and from about 5% to about 10%oxygen, with 90/10 or 95/5 concentrations of helium/oxygen beingpreferred. Another useful reactive atmosphere is a zero gas atmosphere,i.e. room air comprising about 79% nitrogen, about 20% oxygen and smallamounts of other gases, which is also useful for corona treatment tosome extent.

Plasma treating may be conducted in a vacuum chamber or in a chambermaintained at atmospheric conditions. A plasma treatment differs from acorona treatment mainly in that a plasma treatment is conducted in acontrolled, reactive atmosphere of gases, whereas in corona treatmentthe reactive atmosphere is air. The atmosphere in the plasma treater canbe easily controlled and maintained, allowing surface polarity to beachieved in a more controllable and flexible manner than coronatreating. The electric discharge is by radio frequency (RF) energy whichdissociates the gas into electrons, ions, free radicals and metastableproducts. Electrons and free radicals created in the plasma collide withthe fiber surface, rupturing covalent bonds and creating free radicalson the fiber surface. In a batch process, after a predetermined reactiontime or temperature, the process gas and RF energy are turned off andthe leftover gases and other byproducts are removed. In a continuousprocess, which is preferred herein, an array of fibers is passed througha controlled reactive atmosphere comprising atoms, molecules, ionsand/or free radicals of the selected reactive gases, as well as othertrace species. The reactive atmosphere is constantly generated andreplenished, likely reaching a steady state composition, and is notturned off or quenched until the coating machine is stopped.

Plasma treatment may be carried out using any useful commerciallyavailable plasma treating machine, such as plasma treating machinesavailable from Softal Corona & Plasma GmbH & Co of Hamburg, Germany;4^(th) State, Inc of Belmont Calif.; Plasmatreat US LP of Elgin Ill.;Enercon Surface Treating Systems of Milwaukee, Wis. A preferred plasmatreating process is conducted at about atmospheric pressure, i.e. 1 atm(760 mm Hg (760 torr)), with a chamber temperature of about roomtemperature (70° F.-72° F.). The temperature inside the plasma chambermay potentially change due to the treating process, but the temperatureis generally not independently cooled or heated during treatments, andit is not believed to affect the treatment of the fibers as they rapidlypass through the plasma treater. The temperature between the plasmaelectrodes and the fiber web is typically approximately 100° C. Theplasma treating process is preferably conducted under RF power at about0.5 kW to about 3.5 kW, more preferably from about 1.0 kW to about 3.05kW, and most preferably plasma treating is conducted using anatmospheric plasma treater set at 2.0 kW. This power is distributed overthe width of the plasma treating zone (or the length of the electrodes)and this power is also distributed over the length of the substrate orfiber web at a rate that is inversely proportional to the line speed atwhich the fiber web passes through the reactive atmosphere of the plasmatreater. This energy per unit area per unit time (watts per square footper minute or W/SQFT/MIN) or energy flux, is a useful way to comparetreatment levels. Effective values for energy flux are preferably fromabout 0.5 to about 200 Watts/SQFT/MIN, more preferably from about 1 toabout 100 Watts/SQFT/MIN, even more preferably from about 1 to about 80Watts/SQFT/MIN and most preferably from about 2 to about 40Watts/SQFT/MIN. The total gas flow rate is approximately 16 liters/min,but this is not intended to be strictly limiting. The plasma treatmenttime (or residence time) of the fiber is approximately 2 seconds,although this is relative to the dimensions of the plasma treateremployed and is not intended to be strictly limiting. A more appropriatemeasure is the amount of plasma treatment in terms of RF power appliedto the fiber per unit area over time.

Plasma coating is defined as activating the surface of the fiber web andpassing the activated fiber web through an atmosphere containing vinylmonomers, vinyl oligomers or some other reactive species. Plasma coatingcan add very specific chemical functionality to the surface of thefiber, and can add a different polymeric character to the surface of thefiber. In a direct fluorination treatment, the fiber surfaces aremodified by direct fluorination of the fibers with elemental fluorine.For example, the fiber surfaces may be fluorinated by contacting thefiber surfaces with a mixture of 10% F₂/90% He at 25° C. to depositelemental fluorine on said surfaces. The elemental fluorine present onthe fiber surfaces serve as functional groups for bonding withsubsequently applied coating materials. See also, for example, U.S. Pat.Nos. 3,988,491 and 4,020,223, which are incorporated herein byreference, which teach direct fluorination of fibers using a mixture ofelemental fluorine, elemental oxygen and a carrier gas. UV grafting isalso a well known process in the art. In an optional process of UVgrafting of a ballistic fiber surface, the fibers (or fabric) are soakedin a solution of a monomer, photosensitizer and a solvent to at leastpartially coat the fiber/fabric surfaces with the monomer andphotosensitizer. The coated fibers are then irradiated with UVirradiation, as is well known in the art. The particular selection ofmonomer type, photosensitizer type and solvent type will vary as desiredby and readily determined by one skilled in the art. For example,acrylamide groups may be grafted onto UHMWPE polymer chains via anacrylamide grafting monomer, as discussed in the article entitled,“Studies on surface modification of UHMWPE fibers via UV initiatedgrafting” by Jieliang Wang, et al. of the Department of AppliedChemistry, School of Science, Northwestern Polytechnical University,Xi'an, Shaanxi 710072, PR China. Applied Surface Science, Volume 253,Issue 2, 15 Nov. 2006, pages 668-673, the disclosure of which isincorporated herein by reference to the extent consistent herein.

Additionally, the fibers of the invention may be treated with one ormore than one of these of optional treatments. For example, the fibersmay be both roughened by chromic etching and plasma treated, or bothcorona treated and plasma coated, or both plasma treated and plasmacoated. Additionally, composites and fabrics of the invention maycomprise some fibers that are treated and some fibers that are nottreated. For example, composites herein may be fabricated from somefibers that are corona treated and some fibers that are plasma treated,or some fibers that are fluorinated and some fibers that are notfluorinated.

Each of these treatments will be conducted after the at least partialremoval of the fiber surface finish but prior to the application of anybinder/matrix resins or other surface adsorbates/coatings. Treating theexposed fiber surfaces immediately before coating the aligned fiber webwith a polymeric binder material or resin is most preferred because itwill cause the least disruption to the fiber manufacturing process andwill leave the fiber in a modified and unprotected state for theshortest period of time. It is ideal to remove the fiber surface finishand treat the exposed fiber surfaces immediately after unwinding fibersfrom a fiber spool (wound fiber package) and aligning the fibers into afiber web, followed by immediately coating or impregnating the fiberswith a polymer/resin coating. This will also leave the fibers in atreated and uncoated state for the shortest length of time should therebe considerations about the shelf-life or decay rate of the surfacemodification of the fiber. However, this is ideal primarily for causingthe least disruption to the overall fabrication process, and notnecessarily for achieving an improvement in flexural properties or BFSperformance of the composite.

As a result of the at least partial removal of the fiber finish andoptional surface treatments, fibrous composites of the inventioncomprising a plurality of adjoined fiber layers have a preferred stressat yield of at least about 7.50 ksi (˜51.71 MPa), more preferably atleast about 8.0 ksi (˜55.16 MPa), more preferably at least about 8.5 ksi(˜58.61 MPa), more preferably at least about 9.0 ksi (˜62.05 MPa), morepreferably at least about 9.5 ksi (˜65.50 MPa), more preferably at leastabout 10.0 ksi (˜68.95 MPa), more preferably at least about 10.5 ksi(˜72.39 MPa), and most preferably at least about 11.0 ksi (˜75.84 MPa),all being measured on a specimen having a length of approximately 6″(15.24 cm), a width of approximately 0.5″ (12.7 mm)±about 0.02″ (0.508mm), a depth of approximately 0.3″ (7.62 mm) about 0.02″ (0.508 mm), aspan of approximately 4.8″ (12.192 cm), with a strain rate ofapproximately 0.01 in/in/min (with crosshead speed set to 0.128 in/min,as per ASTM D790 Procedure A) and at a standard ambient room temperatureof approximately 72° F. These stress at yield values are relevant tocomposite samples as tested under said conditions and with the abovespecified specimen size and shape. In actual use, a ballistic resistantarticle formed from the fibrous composites of the invention will havevariable sizes and shapes, so the stress at yield values identifiedherein are considered minimum values, not maximum values. The stress atyield (and any other flexural properties referenced in the inventiveexamples) also refers only to measurements taken at approximately roomtemperature (˜72° F.). Warmer conditions may soften the polymeric binderelement of the fibrous composite and reduce the strength of its bondwith the fibers. Any comparative measurements must be taken at the sametesting temperature.

Fibrous composites as described above having said flexural strengthproperties have been found to exhibit significant lower backfacesignature relative to composites having inferior flexural strengthproperties, i.e. composites having a lower stress at yield than thecomposites of the invention. This is particularly evident when thecomponent fibers are polyethylene fibers, which are naturally superiorthan other fibers in their ballistic resistance abilities but have alower natural affinity for polymer coatings. Treating the surfaces ofpolyethylene fibers with any combination of the treatments as describedabove, prior to the fabrication of polyethylene-based fabrics formedtherefrom, to increase the flexural strength of polyethylene-basedcomposites, achieves a combination of structural properties, ballisticpenetration resistance and backface signature resistance properties thatare comparatively superior to any other fiber type, including aramidfibers.

In this regard, the fibrous composites of the invention have a preferredbackface signature of less than about 8 mm as measured for a compositehaving an areal density of 2.0 lb/ft² (psf) when impacted with a124-grain, 9 mm FMJ RN projectile fired at a velocity of from about 427m/s to about 445 m/s (1430 feet/second (fps)±30 fps). This is not to saythat all fibrous composites or articles of the invention will have anareal density of 2.0 psf, nor that all fibrous composites or articles ofthe invention will have a BFS of 8 mm against such an FMJ RN projectileat said velocity. Such only identifies that composites fabricatedaccording to the processes of the invention are characterized in thatwhen fabricated into a 2.0 psf panel, that 2.0 psf panel will have a BFSof less than about 8 mm against such an FMJ RN projectile at saidvelocity. It should also be understood that the terms BFS, backfacedeformation, trauma signature and blunt force trauma are not measures ofthe depth of depression of the composite due to projectile impact, butrather are measures of the depth of depression in a backing material orinto a user body due to projectile impact. This is particularly relevantfor the study of hard armor, particularly helmet armor, as helmet BFS istypically tested by placing a prototype helmet on a metallic head form,where the helmet is held on the head form by a suspension system thatseparates the helmet from the head form by ½ inch (1.27 cm). Sections ofthe head form are filled with clay, and the depth of depression in thoseclay areas is measured as the BFS without including the ½ inch spacingdepth in the measurement. This is done for the purpose of correlatingthe laboratory BFS testing with actual BFS experienced by a soldier infield use, where a typical helmet incorporates a typical ½ inch offsetfrom the head, due to helmet interior padding or a suspensionsystem/retention harness. The BFS of soft armor, on the other hand, isconventionally tested by placing the armor directly on the clay surfacewith no spacing, which is consistent with its position in actual fielduse. Accordingly, BFS depth measurements are relative to the test methodused, and when comparing BFS depth measurements, it is necessary toidentify whether or not the test method used required positioning thetest sample directly on a backing material or spaced from the backingmaterial. In this regard, BFS testing of the fibrous composites of theinvention were all measured with a ½ inch space between the 2.0 psfsample and a clay backing material. In the preferred embodiments of theinvention, the fibrous composites of the invention have a more preferredbackface signature of less than about 7 mm when impacted with a124-grain, 9 mm FMJ projectile fired at a velocity of from about 427 m/sto about 445 m/s under the projectile firing conditions of NIJ Standard0101.04, more preferably less than about 6 mm, more preferably less thanabout 5 mm, more preferably less than about 4 mm, more preferably lessthan about 3 mm, more preferably less than about 2 mm, and mostpreferably have a backface signature of less than about 1 mm whenimpacted with a 124-grain, 9 mm FMJ RN projectile (a bullet comprisingapproximately 90% copper and 10% zinc excluding the base) fired at avelocity of from about 427 m/s to about 445 m/s. Testing BFS against a124-grain, 9 mm FMJ RN projectile fired at a velocity of from about 427m/s to about 445 m/s is common in the art.

Said fibrous composites achieving these BFS values each comprise aplurality of adjoined fiber layers, each fiber layer comprising fibershaving surfaces that are at least partially covered with a polymericmaterial, wherein said fibers are predominantly free of a fiber surfacefinish such that said polymeric material is predominantly in directcontact with the fiber surfaces, and have a stress at yield at aboutroom temperature of at least about 7.50 ksi (˜51.71 MPa), morepreferably at least about 8.0 ksi (˜55.16 MPa), more preferably at leastabout 8.5 ksi (˜58.61 MPa), more preferably at least about 9.0 ksi(˜62.05 MPa), more preferably at least about 9.5 ksi (˜65.50 MPa), morepreferably at least about 10.0 ksi (˜68.95 MPa), more preferably atleast about 10.5 ksi (˜72.39 MPa), and most preferably at least about11.0 ksi (˜75.84 MPa) as per ASTM D790 for a specimen sample asdescribed above. Said fibrous composites achieving both these BFS valuesand such stress at yield properties also preferably exhibit a V₅₀against a 17-grain fragment simulating projectile (FSP) of at leastabout 1750 feet/sec (fps) (533.40 m/s), more preferably at least about1800 fps (548.64 m/s), even more preferably at least about 1850 fps(563.88 m/s) and most preferably at least about 1900 fps (579.12 m/s).All of the above V₅₀ values are for armor panels having a compositeareal density of approximately 1.0 lbs/ft² (psf)(4.88 kg/m² (ksm)). Allof the above BFS values are for armor panels having a composite arealdensity of approximately 2.0 lbs/ft² (psf)(7.96 kg/m² (ksm)). As withBFS, this is not to say that all fibrous composites or articles of theinvention will have a particular areal density, nor that all fibrouscomposites or articles of the invention will have a V₅₀ against a17-grain FSP of at least about 1750 feet/sec. Such only identifies thatcomposites fabricated according to the processes of the invention arecharacterized in that when fabricated into a 1.0 psf panel, that 1.0 psfpanel will have a V₅₀ against a 17-grain FSP of at least about 1750feet/sec.

The fiber layers and composites formed herein are preferably ballisticresistant composites formed from high-strength, high tensile moduluspolymeric fibers. Most preferably, the fibers comprise high strength,high tensile modulus fibers which are useful for the formation ofballistic resistant materials and articles. As used herein, a“high-strength, high tensile modulus fiber” is one which has a preferredtenacity of at least about 7 g/denier or more, a preferred tensilemodulus of at least about 150 g/denier or more, and preferably anenergy-to-break of at least about 8 J/g or more, each both as measuredby ASTM D2256. As used herein, the term “denier” refers to the unit oflinear density, equal to the mass in grams per 9000 meters of fiber oryarn. As used herein, the term “tenacity” refers to the tensile stressexpressed as force (grams) per unit linear density (denier) of anunstressed specimen. The “initial modulus” of a fiber is the property ofa material representative of its resistance to deformation. The term“tensile modulus” refers to the ratio of the change in tenacity,expressed in grams-force per denier (g/d) to the change in strain,expressed as a fraction of the original fiber length (in/in).

The polymers forming the fibers are preferably high-strength, hightensile modulus fibers suitable for the manufacture of ballisticresistant composites/fabrics. Particularly suitable high-strength, hightensile modulus fiber materials that are particularly suitable for theformation of ballistic resistant composites and articles includepolyolefin fibers, including high density and low density polyethylene.Particularly preferred are extended chain polyolefin fibers, such ashighly oriented, high molecular weight polyethylene fibers, particularlyultra-high molecular weight polyethylene fibers, and polypropylenefibers, particularly ultra-high molecular weight polypropylene fibers.Also suitable are aramid fibers, particularly para-aramid fibers,polyamide fibers, polyethylene terephthalate fibers, polyethylenenaphthalate fibers, extended chain polyvinyl alcohol fibers, extendedchain polyacrylonitrile fibers, polybenzazole fibers, such aspolybenzoxazole (PBO) and polybenzothiazole (PBT) fibers, liquid crystalcopolyester fibers and other rigid rod fibers such as M5® fibers. Eachof these fiber types is conventionally known in the art. Also suitablefor producing polymeric fibers are copolymers, block polymers and blendsof the above materials.

The most preferred fiber types for ballistic resistant fabrics includepolyethylene, particularly extended chain polyethylene fibers, aramidfibers, polybenzazole fibers, liquid crystal copolyester fibers,polypropylene fibers, particularly highly oriented extended chainpolypropylene fibers, polyvinyl alcohol fibers, polyacrylonitrile fibersand other rigid rod fibers, particularly M5® fibers. Specifically mostpreferred fibers are aramid fibers.

In the case of polyethylene, preferred fibers are extended chainpolyethylenes having molecular weights of at least 500,000, preferablyat least one million and more preferably between two million and fivemillion. Such extended chain polyethylene (ECPE) fibers may be grown insolution spinning processes such as described in U.S. Pat. Nos.4,137,394 or 4,356,138, which are incorporated herein by reference, ormay be spun from a solution to form a gel structure, such as describedin U.S. Pat. Nos. 4,551,296 and 5,006,390, which are also incorporatedherein by reference. A particularly preferred fiber type for use in theinvention are polyethylene fibers sold under the trademark SPECTRA® fromHoneywell International Inc. SPECTRA® fibers are well known in the artand are described, for example, in U.S. Pat. Nos. 4,623,547 and4,748,064. In addition to polyethylene, another useful polyolefin fibertype is polypropylene (fibers or tapes), such as TEGRIS® fiberscommercially available from Milliken & Company of Spartanburg, S.C.

Also particularly preferred are aramid (aromatic polyamide) orpara-aramid fibers. Such are commercially available and are described,for example, in U.S. Pat. No. 3,671,542. For example, usefulpoly(p-phenylene terephthalamide) filaments are produced commercially byDuPont under the trademark of KEVLAR®. Also useful in the practice ofthis invention are poly(m-phenylene isophthalamide) fibers producedcommercially by DuPont under the trademark NOMEX® and fibers producedcommercially by Teijin under the trademark TWARON®; aramid fibersproduced commercially by Kolon Industries, Inc. of Korea under thetrademark HERACRON®; p-aramid fibers SVM™ and RUSAR™ which are producedcommercially by Kamensk Volokno JSC of Russia and ARMOS™ p-aramid fibersproduced commercially by JSC Chim Volokno of Russia.

Suitable polybenzazole fibers for the practice of this invention arecommercially available and are disclosed for example in U.S. Pat. Nos.5,286,833, 5,296,185, 5,356,584, 5,534,205 and 6,040,050, each of whichis incorporated herein by reference. Suitable liquid crystal copolyesterfibers for the practice of this invention are commercially available andare disclosed, for example, in U.S. Pat. Nos. 3,975,487; 4,118,372 and4,161,470, each of which is incorporated herein by reference. Suitablepolypropylene fibers include highly oriented extended chainpolypropylene (ECPP) fibers as described in U.S. Pat. No. 4,413,110,which is incorporated herein by reference. Suitable polyvinyl alcohol(PV-OH) fibers are described, for example, in U.S. Pat. Nos. 4,440,711and 4,599,267 which are incorporated herein by reference. Suitablepolyacrylonitrile (PAN) fibers are disclosed, for example, in U.S. Pat.No. 4,535,027, which is incorporated herein by reference. Each of thesefiber types is conventionally known and is widely commerciallyavailable.

M5® fibers are formed from pyridobisimidazole-2,6-diyl(2,5-dihydroxy-p-phenylene) and are manufactured by Magellan SystemsInternational of Richmond, Va. and are described, for example, in U.S.Pat. Nos. 5,674,969, 5,939,553, 5,945,537, and 6,040,478, each of whichis incorporated herein by reference. Also suitable are combinations ofall the above materials, all of which are commercially available. Forexample, the fibrous layers may be formed from a combination of one ormore of aramid fibers, UHMWPE fibers (e.g. SPECTRA® fibers), carbonfibers, etc., as well as fiberglass and other lower-performingmaterials. However, BFS and V₅₀ values may vary by fiber type.

The fibers may be of any suitable denier, such as, for example, 50 toabout 3000 denier, more preferably from about 200 to 3000 denier, stillmore preferably from about 650 to about 2000 denier, and most preferablyfrom about 800 to about 1500 denier. The selection is governed byconsiderations of ballistic effectiveness and cost. Finer fibers aremore costly to manufacture and to weave, but can produce greaterballistic effectiveness per unit weight.

As stated above, a high-strength, high tensile modulus fiber is onewhich has a preferred tenacity of about 7 g/denier or more, a preferredtensile modulus of about 150 g/denier or more and a preferredenergy-to-break of about 8 J/g or more, each as measured by ASTM D2256.In the preferred embodiment of the invention, the tenacity of the fibersshould be about 15 g/denier or more, preferably about 20 g/denier ormore, more preferably about 25 g/denier, still more preferably about 30g/denier or more, still more preferably about 37 g/denier or more stillmore preferably about 40 g/denier or more still more preferably about 45g/denier or more still more preferably about 50 g/denier or more stillmore preferably about 55 g/denier or more and most preferably about 60g/denier or more. Preferred fibers also have a preferred tensile modulusof about 300 g/denier or more, more preferably about 400 g/denier ormore, more preferably about 500 g/denier or more, more preferably about1,000 g/denier or more and most preferably about 1,500 g/denier or more.Preferred fibers also have a preferred energy-to-break of about 15 J/gor more, more preferably about 25 J/g or more, more preferably about 30J/g or more and most preferably have an energy-to-break of about 40 J/gor more. These combined high strength properties are obtainable byemploying well known processes. U.S. Pat. Nos. 4,413,110, 4,440,711,4,535,027, 4,457,985, 4,623,547 4,650,710 and 4,748,064 generallydiscuss the formation of preferred high strength, extended chainpolyethylene fibers. Such methods, including solution grown or gel fiberprocesses, are well known in the art. Methods of forming each of theother preferred fiber types, including para-aramid fibers, are alsoconventionally known in the art, and the fibers are commerciallyavailable. The fibrous composites of the invention also preferablycomprise fibers having a fiber areal density of about 1.7 g/cm³ or less.

After removing at least a portion of the fiber surface finish from thefiber surfaces as desired, and after the fiber surfaces are optionallytreated under conditions effective to enhance the adsorbability of asubsequently applied adsorbate on the fiber surfaces, an adsorbate isthen optionally applied onto at least a portion of at least some of thefibers. As used herein, the term “adsorption” (or “adsorbability” or“adsorb”) is broadly intended to encompass both physisorption andchemisorption of any material (solid, liquid, gas or plasma) on thefiber surface, where “physisorption” is defined herein as physicalbonding of a material on a fiber surface and “chemisorption” is definedherein as chemical bonding of a material on a fiber surface, where achemical reaction occurs at the exposed fiber (i.e. the adsorbant)surface. The term “adsorption” as used herein is intended to include anypossible means of attaching, adhering or bonding a material to asubstrate surface, physically or chemically, without limitation,including means for increasing fiber wetting/adhesion of fibers inpolymer matrices. This expressly includes the adhesion or coating of anysolid, liquid or gas material on the fiber surfaces, including anymonomer, oligomer, polymer or resin, and including the application ofany organic material or inorganic material onto the fiber surfaces. Inthis regard, the definition of “adsorbate” is also not intended to belimiting and expressly includes all polymers useful as polymer bindermaterials, resins or polymeric matrix materials. However, for thepurposes of this invention, the class of useful adsorbates expresslyexcludes materials that do not have binding properties, including fibersurface finish substances such as a spin finish materials, which are notbinder materials having binding properties and which, to the contrary,are specifically removed from fiber surfaces according to the invention.

For the purposes of the invention, the application of a polymer bindermaterial adsorbate, such as a resin, is required to achieve a compositehaving the desired flexural properties. Accordingly, the fibers formingthe woven or non-woven fabrics of the invention are coated with orimpregnated with a polymeric binder material. The polymeric bindermaterial either partially or substantially coats the individual fibersof the fiber layers, preferably substantially coating each of theindividual fibers of each fiber layer. The polymeric binder material isalso commonly known in the art as a “polymeric matrix” material, andthese terms are used interchangeably herein. These terms areconventionally known in the art and describe a material that bindsfibers together either by way of its inherent adhesive characteristicsor after being subjected to well known heat and/or pressure conditions.Such a “polymeric matrix” or “polymeric binder” material may alsoprovide a fabric with other desirable properties, such as abrasionresistance and resistance to deleterious environmental conditions, so itmay be desirable to coat the fibers with such a binder material evenwhen its binding properties are not important, such as with wovenfabrics.

Suitable polymeric binder materials include both low modulus,elastomeric materials and high modulus, rigid materials. As used hereinthroughout, the term tensile modulus means the modulus of elasticity asmeasured by ASTM 2256 for a fiber and by ASTM D638 for a polymericbinder material. A low or high modulus binder may comprise a variety ofpolymeric and non-polymeric materials. A preferred polymeric bindercomprises a low modulus elastomeric material. For the purposes of thisinvention, a low modulus elastomeric material has a tensile modulusmeasured at about 6,000 psi (41.4 MPa) or less according to ASTM D638testing procedures. A low modulus polymer preferably has, the tensilemodulus of the elastomer is about 4,000 psi (27.6 MPa) or less, morepreferably about 2400 psi (16.5 MPa) or less, more preferably 1200 psi(8.23 MPa) or less, and most preferably is about 500 psi (3.45 MPa) orless. The glass transition temperature (Tg) of the elastomer ispreferably less than about 0° C., more preferably the less than about−40° C., and most preferably less than about −50° C. The elastomer alsohas a preferred elongation to break of at least about 50%, morepreferably at least about 100% and most preferably has an elongation tobreak of at least about 300%.

A wide variety of materials and formulations having a low modulus may beutilized as the polymeric binder. Representative examples includepolybutadiene, polyisoprene, natural rubber, ethylene-propylenecopolymers, ethylene-propylene-diene terpolymers, polysulfide polymers,polyurethane elastomers, chlorosulfonated polyethylene, polychloroprene,plasticized polyvinylchloride, butadiene acrylonitrile elastomers,poly(isobutylene-co-isoprene), polyacrylates, polyesters, polyethers,fluoroelastomers, silicone elastomers, copolymers of ethylene,polyamides (useful with some fiber types), acrylonitrile butadienestyrene, polycarbonates, and combinations thereof, as well as other lowmodulus polymers and copolymers curable below the melting point of thefiber. Also preferred are blends of different elastomeric materials, orblends of elastomeric materials with one or more thermoplastics.

Particularly useful are block copolymers of conjugated dienes and vinylaromatic monomers. Butadiene and isoprene are preferred conjugated dieneelastomers. Styrene, vinyl toluene and t-butyl styrene are preferredconjugated aromatic monomers. Block copolymers incorporatingpolyisoprene may be hydrogenated to produce thermoplastic elastomershaving saturated hydrocarbon elastomer segments. The polymers may besimple tri-block copolymers of the type A-B-A, multi-block copolymers ofthe type (AB)_(n) (n=2-10) or radial configuration copolymers of thetype R-(BA)_(x) (x=3-150); wherein A is a block from a polyvinylaromatic monomer and B is a block from a conjugated diene elastomer.Many of these polymers are produced commercially by Kraton Polymers ofHouston, Tex. and described in the bulletin “Kraton ThermoplasticRubber”, SC-68-81. Also useful are resin dispersions ofstyrene-isoprene-styrene (SIS) block copolymer sold under the trademarkPRINLIN® and commercially available from Henkel Technologies, based inDüsseldorf, Germany. Particularly preferred low modulus polymeric binderpolymers comprise styrenic block copolymers sold under the trademarkKRATON® commercially produced by Kraton Polymers. A particularlypreferred polymeric binder material comprises apolystyrene-polyisoprene-polystyrene-block copolymer sold under thetrademark KRATON®.

While low modulus polymeric matrix binder materials are most useful forthe formation of flexible armor, such as ballistic resistant vests, highmodulus, rigid materials useful for forming hard armor articles, such ashelmets, are particularly preferred herein. Preferred high modulus,rigid materials generally have a higher initial tensile modulus than6,000 psi. Preferred high modulus, rigid polymeric binder materialsuseful herein include polyurethanes (both ether and ester based),epoxies, polyacrylates, phenolic/polyvinyl butyral (PVB) polymers, vinylester polymers, styrene-butadiene block copolymers, as well as mixturesof polymers such as vinyl ester and diallyl phthalate or phenolformaldehyde and polyvinyl butyral. A particularly preferred rigidpolymeric binder material for use in this invention is a thermosettingpolymer, preferably soluble in carbon-carbon saturated solvents such asmethyl ethyl ketone, and possessing a high tensile modulus when cured ofat least about 1×10⁶ psi (6895 MPa) as measured by ASTM D638.Particularly preferred rigid polymeric binder materials are thosedescribed in U.S. Pat. No. 6,642,159, the disclosure of which isincorporated herein by reference. The polymeric binder, whether a lowmodulus material or a high modulus material, may also include fillerssuch as carbon black or silica, may be extended with oils, or may bevulcanized by sulfur, peroxide, metal oxide or radiation cure systems asis well known in the art.

Most specifically preferred are polar resins or polar polymers,particularly polyurethanes within the range of both soft and rigidmaterials at a tensile modulus ranging from about 2,000 psi (13.79 MPa)to about 8,000 psi (55.16 MPa). Preferred polyurethanes are applied asaqueous polyurethane dispersions that are most preferably, but notnecessarily, cosolvent free. Such includes aqueous anionic polyurethanedispersions, aqueous cationic polyurethane dispersions and aqueousnonionic polyurethane dispersions. Particularly preferred are aqueousanionic polyurethane dispersions; aqueous aliphatic polyurethanedispersions, and most preferred are aqueous anionic, aliphaticpolyurethane dispersions, all of which are preferably cosolvent freedispersions. Such includes aqueous anionic polyester-based polyurethanedispersions; aqueous aliphatic polyester-based polyurethane dispersions;and aqueous anionic, aliphatic polyester-based polyurethane dispersions,all of which are preferably cosolvent free dispersions. Such alsoincludes aqueous anionic polyether polyurethane dispersions; aqueousaliphatic polyether-based polyurethane dispersions; and aqueous anionic,aliphatic polyether-based polyurethane dispersions, all of which arepreferably cosolvent free dispersions. Similarly preferred are allcorresponding variations (polyester-based; aliphatic polyester-based;polyether-based; aliphatic polyether-based, etc.) of aqueous cationicand aqueous nonionic dispersions. Most preferred is an aliphaticpolyurethane dispersion having a modulus at 100% elongation of about 700psi or more, with a particularly preferred range of 700 psi to about3000 psi. More preferred are aliphatic polyurethane dispersions having amodulus at 100% elongation of about 1000 psi or more, and still morepreferably about 1100 psi or more. Most preferred is an aliphatic,polyether-based anionic polyurethane dispersion having a modulus of 1000psi or more, preferably 1100 psi or more.

The rigidity, impact and ballistic properties of the articles formedfrom the composites of the invention are affected by the tensile modulusof the polymeric binder polymer coating the fibers. For example, U.S.Pat. No. 4,623,574 discloses that fiber reinforced compositesconstructed with elastomeric matrices having tensile moduli less thanabout 6,000 psi (41,300 kPa) have superior ballistic properties comparedboth to composites constructed with higher modulus polymers, and alsocompared to the same fiber structure without a polymeric bindermaterial. However, low tensile modulus polymeric binder materialpolymers also yield lower rigidity composites. Further, in certainapplications, particularly those where a composite must function in bothanti-ballistic and structural modes, there is needed a superiorcombination of ballistic resistance and rigidity. Accordingly, the mostappropriate type of polymeric binder polymer to be used will varydepending on the type of article to be formed from the composites of theinvention. In order to achieve a compromise in both properties, asuitable polymeric binder may combine both low modulus and high modulusmaterials to form a single polymeric binder.

The polymeric binder material may be applied either simultaneously orsequentially to a plurality of fibers arranged as a fiber web (e.g. aparallel array or a felt) to form a coated web, applied to a wovenfabric to form a coated woven fabric, or as another arrangement, tothereby impregnate the fiber layers with the binder. As used herein, theterm “impregnated with” is synonymous with “embedded in” as well as“coated with” or otherwise applied with the coating where the bindermaterial diffuses into the fiber layer and is not simply on a surface ofthe fiber layers. The polymeric material may also be applied onto atleast one array of fibers that is not part of a fiber web, followed byweaving the fibers into a woven fabric or followed by formulating anon-woven fabric following the methods described previously herein.Techniques of forming woven and non-woven fiber plies, layers andfabrics are well known in the art.

Although not required, fibers forming woven fiber layers are at leastpartially coated with a polymeric binder, followed by a consolidationstep similar to that conducted with non-woven fiber layers. Such aconsolidation step may be conducted to merge multiple woven fiber layerswith each other, or to further merge the binder with the fibers of saidwoven fabric. For example, a plurality of woven fiber layers do notnecessarily have to be consolidated, and may be attached by other means,such as with a conventional adhesive, or by stitching.

Generally, a polymeric binder coating is necessary to efficiently merge,i.e. consolidate, a plurality of non-woven fiber plies. The polymericbinder material may be applied onto the entire surface area of theindividual fibers or only onto a partial surface area of the fibers.Most preferably, the coating of the polymeric binder material is appliedonto substantially all the surface area of each individual fiber forminga fiber layer of the invention. Where a fiber layer comprises aplurality of yarns, each fiber forming a single strand of yarn ispreferably coated with the polymeric binder material.

Any appropriate application method may be utilized to apply thepolymeric binder material and the term “coated” is not intended to limitthe method by which it is applied onto the filaments/fibers. Thepolymeric binder material is applied directly onto the fiber surfacesusing any appropriate method that would be readily determined by oneskilled in the art, and the binder then typically diffuses into thefiber layer as discussed herein. For example, the polymeric bindermaterials may be applied in solution, emulsion or dispersion form byspraying, extruding or roll coating a solution of the polymer materialonto fiber surfaces, wherein a portion of the solution comprises thedesired polymer or polymers and a portion of the solution comprises asolvent capable of dissolving or dispersing the polymer or polymers,followed by drying. Alternately, the polymeric binder material may beextruded onto the fibers using conventionally known techniques, such asthrough a slot-die, or through other techniques such as direct gravure,Meyer rod and air knife systems, which are well known in the art.Another method is to apply a neat polymer of the binder material ontofibers either as a liquid, a sticky solid or particles in suspension oras a fluidized bed. Alternatively, the coating may be applied as asolution, emulsion or dispersion in a suitable solvent which does notadversely affect the properties of fibers at the temperature ofapplication. For example, the fibers can be transported through asolution of the polymeric binder material to substantially coat thefibers and then dried.

In another coating technique, the fibers may be dipped into a bath of asolution containing the polymeric binder material dissolved or dispersedin a suitable solvent, and then dried through evaporation orvolatilization of the solvent. This method preferably at least partiallycoats each individual fiber with the polymeric material, preferablysubstantially coating or encapsulating each of the individual fibers andcovering all or substantially all of the filament/fiber surface areawith the polymeric binder material. The dipping procedure may berepeated several times as required to place a desired amount of polymermaterial onto the fibers.

Other techniques for applying a coating to the fibers may be used,including coating of a gel fiber precursor when appropriate, such as bypassing the gel fiber through a solution of the appropriate coatingpolymer under conditions to attain the desired coating. Alternatively,the fibers may be extruded into a fluidized bed of an appropriatepolymeric powder.

While it is necessary that the fibers be coated with a polymeric binderafter the at least partial removal of the fiber surface finish, andpreferably after a surface treatment that enhances the adsorbability ofa subsequently applied adsorbate on the fiber surfaces, the fibers maybe coated with the polymeric binder either before or after the fibersare arranged into one or more plies/layers, or before or after thefibers are woven into a woven fabric. Woven fabrics may be formed usingtechniques that are well known in the art using any fabric weave, suchas plain weave, crowfoot weave, basket weave, satin weave, twill weaveand the like. Plain weave is most common, where fibers are woventogether in an orthogonal 0°/90° orientation. Either prior to or afterweaving, the individual fibers of each woven fabric material may or maynot be coated with the polymeric binder material. Typically, weaving offabrics is performed prior to coating fibers with the polymeric binder,where the woven fabrics are thereby impregnated with the binder.However, the invention is not intended to be limited by the stage atwhich the polymeric binder is applied to the fibers, nor by the meansused to apply the polymeric binder.

Methods for the production of non-woven fabrics are well known in theart. In the preferred embodiments herein, a plurality of fibers arearranged into at least one array, typically being arranged as a fiberweb comprising a plurality of fibers aligned in a substantiallyparallel, unidirectional array. As previously stated, in a typicalprocess for forming non-woven unidirectionally aligned fiber plies,fiber bundles are supplied from a creel and led through guides and oneor more spreader bars into a collimating comb, followed by coating thefibers with a polymeric binder material. A typical fiber bundle willhave from about 30 to about 2000 individual fibers. The spreader barsand collimating comb disperse and spread out the bundled fibers,reorganizing them side-by-side in a coplanar fashion. Ideal fiberspreading results in the individual filaments or individual fibers beingpositioned next to one another in a single fiber plane, forming asubstantially unidirectional, parallel array of fibers without fibersoverlapping each other. At this point, removing the fiber surface finishbefore or during this spreading step may enhance and accelerate thespreading of the fibers into such a parallel array.

After the fibers are coated with the binder material, the coated fibersare formed into non-woven fiber layers that comprise a plurality ofoverlapping, non-woven fiber plies that are consolidated into asingle-layer, monolithic element. In a preferred non-woven fabricstructure of the invention, a plurality of stacked, overlapping unitapesare formed wherein the parallel fibers of each single ply (unitape) arepositioned orthogonally to the parallel fibers of each adjacent singleply relative to the longitudinal fiber direction of each single ply. Thestack of overlapping non-woven fiber plies is consolidated under heatand pressure, or by adhering the coatings of individual fiber plies, toform a single-layer, monolithic element which has also been referred toin the art as a single-layer, consolidated network where a “consolidatednetwork” describes a consolidated (merged) combination of fiber plieswith the polymeric matrix/binder. Articles of the invention may alsocomprise hybrid consolidated combinations of woven fabrics and non-wovenfabrics, as well as combinations of non-woven fabrics formed fromunidirectional fiber plies and non-woven felt fabrics.

Most typically, non-woven fiber layers or fabrics include from 1 toabout 6 plies, but may include as many as about 10 to about 20 plies asmay be desired for various applications. The greater the number of pliestranslates into greater ballistic resistance, but also greater weight.Accordingly, the number of fiber plies forming a fiber layer compositeand/or fabric composite or an article of the invention varies dependingupon the ultimate use of the fabric or article. For example, in bodyarmor vests for military applications, in order to form an articlecomposite that achieves a desired 1.0 pound per square foot or lessareal density (4.9 kg/m²), a total of about 100 plies (or layers) toabout 50 individual plies (or layers) may be required, wherein theplies/layers may be woven, knitted, felted or non-woven fabrics (withparallel oriented fibers or other arrangements) formed from thehigh-strength fibers described herein. In another embodiment, body armorvests for law enforcement use may have a number of plies/layers based onthe NIJ threat level. For example, for an NIJ Threat Level IIIA vest,there may be a total of 40 plies. For a lower NIJ Threat Level, fewerplies/layers may be employed. The invention allows for the incorporationof a greater number of fiber plies to achieve the desired level ofballistic protection without increasing the fabric weight as compared toother known ballistic resistant structures.

As is conventionally known in the art, excellent ballistic resistance isachieved when individual fiber plies are cross-plied such that the fiberalignment direction of one ply is rotated at an angle with respect tothe fiber alignment direction of another ply. Most preferably, the fiberplies are cross-plied orthogonally at 0° and 90° angles, but adjacentplies can be aligned at virtually any angle between about 0° and about90° with respect to the longitudinal fiber direction of another ply. Forexample, a five ply non-woven structure may have plies oriented at a0°/45°/90°/45°/0° or at other angles. Such rotated unidirectionalalignments are described, for example, in U.S. Pat. Nos. 4,457,985;4,748,064; 4,916,000; 4,403,012; 4,623,574; and 4,737,402, all of whichare incorporated herein by reference to the extent not incompatibleherewith.

Methods of consolidating fiber plies to form fiber layers and compositesare well known, such as by the methods described in U.S. Pat. No.6,642,159. Consolidation can occur via drying, cooling, heating,pressure or a combination thereof. Heat and/or pressure may not benecessary, as the fibers or fabric layers may just be glued together, asis the case in a wet lamination process. Typically, consolidation isdone by positioning the individual fiber plies on one another underconditions of sufficient heat and pressure to cause the plies to combineinto a unitary fabric. Consolidation may be done at temperatures rangingfrom about 50° C. to about 175° C., preferably from about 105° C. toabout 175° C., and at pressures ranging from about 5 psig (0.034 MPa) toabout 2500 psig (17 MPa), for from about 0.01 seconds to about 24 hours,preferably from about 0.02 seconds to about 2 hours. When heating, it ispossible that the polymeric binder coating can be caused to stick orflow without completely melting. However, generally, if the polymericbinder material (if it is one that is capable of melting) is caused tomelt, relatively little pressure is required to form the composite,while if the binder material is only heated to a sticking point, morepressure is typically required. As is conventionally known in the art,consolidation may be conducted in a calender set, a flat-bed laminator,a press or in an autoclave. Most commonly, a plurality of orthogonalfiber webs are “glued” together with the binder polymer and run througha flat bed laminator to improve the uniformity and strength of the bond.Further, the consolidation and polymer application/bonding steps maycomprise two separate steps or a single consolidation/lamination step.

Alternately, consolidation may be achieved by molding under heat andpressure in a suitable molding apparatus. Generally, molding isconducted at a pressure of from about 50 psi (344.7 kPa) to about 5,000psi (34,470 kPa), more preferably about 100 psi (689.5 kPa) to about3,000 psi (20,680 kPa), most preferably from about 150 psi (1,034 kPa)to about 1,500 psi (10,340 kPa). Molding may alternately be conducted athigher pressures of from about 5,000 psi (34,470 kPa) to about 15,000psi (103,410 kPa), more preferably from about 750 psi (5,171 kPa) toabout 5,000 psi, and more preferably from about 1,000 psi to about 5,000psi. The molding step may take from about 4 seconds to about 45 minutes.Preferred molding temperatures range from about 200° F. (˜93° C.) toabout 350° F. (˜177° C.), more preferably at a temperature from about200° F. to about 300° F. and most preferably at a temperature from about200° F. to about 280° F. The pressure under which the fiber layers andfabric composites of the invention are molded typically has a directeffect on the stiffness or flexibility of the resulting molded product.Molding at a higher pressure generally produces stiffer materials, up toa certain limit. In addition to the molding pressure, the quantity,thickness and composition of the fiber plies and polymeric bindercoating type also directly affects the stiffness of the articles formedfrom the composites.

While each of the molding and consolidation techniques described hereinare similar, each process is different. Particularly, molding is a batchprocess and consolidation is a generally continuous process. Further,molding typically involves the use of a mold, such as a shaped mold or amatch-die mold when forming a flat panel, and does not necessarilyresult in a planar product. Normally consolidation is done in a flat-bedlaminator, a calendar nip set or as a wet lamination to produce soft(flexible) body armor fabrics. Molding is typically reserved for themanufacture of hard armor, e.g. rigid plates. In either process,suitable temperatures, pressures and times are generally dependent onthe type of polymeric binder coating materials, polymeric bindercontent, process used and fiber type.

To produce a fabric article having sufficient ballistic resistanceproperties, the total weight of the binder/matrix coating preferablycomprises from about 2% to about 50% by weight, more preferably fromabout 5% to about 30%, more preferably from about 7% to about 20%, andmost preferably from about 11% to about 16% by weight of the fibers plusthe weight of the coating, wherein 16% is most preferred for non-wovenfabrics. A lower binder/matrix content is appropriate for woven fabrics,wherein a polymeric binder content of greater than zero but less than10% by weight of the fibers plus the weight of the coating is typicallymost preferred. This is not intended as limiting. For example,phenolic/PVB impregnated woven aramid fabrics are sometimes fabricatedwith a higher resin content of from about 20% to about 30%, althougharound 12% content is typically preferred.

Following weaving or consolidation of the fiber layers, an optionalthermoplastic polymer layer may be attached to one or both of the outersurfaces of the fibrous composite via conventional methods. Suitablepolymers for the thermoplastic polymer layer non-exclusively includethermoplastic polymers non-exclusively may be selected from the groupconsisting of polyolefins, polyamides, polyesters (particularlypolyethylene terephthalate (PET) and PET copolymers), polyurethanes,vinyl polymers, ethylene vinyl alcohol copolymers, ethylene octanecopolymers, acrylonitrile copolymers, acrylic polymers, vinyl polymers,polycarbonates, polystyrenes, fluoropolymers and the like, as well asco-polymers and mixtures thereof, including ethylene vinyl acetate (EVA)and ethylene acrylic acid. Also useful are natural and synthetic rubberpolymers. Of these, polyolefin and polyamide layers are preferred. Thepreferred polyolefin is a polyethylene. Non-limiting examples of usefulpolyethylenes are low density polyethylene (LDPE), linear low densitypolyethylene (LLDPE), Medium Density Polyethylene (MDPE), linear mediumdensity polyethylene (LMDPE), linear very-low density polyethylene(VLDPE), linear ultra-low density polyethylene (ULDPE), high densitypolyethylene (HDPE) and co-polymers and mixtures thereof. Also usefulare SPUNFAB® polyamide webs commercially available from Spunfab, Ltd, ofCuyahoga Falls, Ohio (trademark registered to Keuchel Associates, Inc.),as well as THERMOPLAST™ and HELIOPLAST™ webs, nets and films,commercially available from Protechnic S.A. of Cernay, France. Thethermoplastic polymer layer may be bonded to the composite surfacesusing well known techniques, such as thermal lamination. Typically,laminating is done by positioning the individual layers on one anotherunder conditions of sufficient heat and pressure to cause the layers tocombine into a unitary film. The individual layers are positioned on oneanother, and the combination is then typically passed through the nip ofa pair of heated laminating rollers by techniques well known in the art.Lamination heating may be conducted at temperatures ranging from about95° C. to about 175° C., preferably from about 105° C. to about 175° C.,at pressures ranging from about 5 psig (0.034 MPa) to about 100 psig(0.69 MPa), for from about 5 seconds to about 36 hours, preferably fromabout 30 seconds to about 24 hours.

The thickness of the individual fabrics/composites/fiber layers willcorrespond to the thickness of the individual fibers and the number offiber layers incorporated into a fabric. A preferred woven fabric willhave a preferred thickness of from about 25 μm to about 600 μm perlayer, more preferably from about 50 μm to about 385 μm and mostpreferably from about 75 μm to about 255 μm per layer. A preferrednon-woven fabric, i.e. a non-woven, single-layer, consolidated network,will have a preferred thickness of from about 12 μm to about 600 μm,more preferably from about 50 μm to about 385 μm and most preferablyfrom about 75 μm to about 255 μm, wherein a single-layer, consolidatednetwork typically includes two consolidated plies (i.e. two unitapes).Any thermoplastic polymer layers are preferably very thin, havingpreferred layer thicknesses of from about 1 μm to about 250 μm, morepreferably from about 5 μm to about 25 μm and most preferably from about5 μm to about 9 μm. Discontinuous webs such as SPUNFAB® non-woven websare preferably applied with a basis weight of 6 grams per square meter(gsm). While such thicknesses are preferred, it is to be understood thatother thicknesses may be produced to satisfy a particular need and yetfall within the scope of the present invention.

The fabrics/composites of the invention will have a preferred arealdensity prior to consolidation/molding of from about 20 grams/m² (0.004lb/ft² (psf)) to about 1000 gsm (0.2 psf). More preferable arealdensities for the fabrics/composites of this invention prior toconsolidation/molding will range from about 30 gsm (0.006 psf) to about500 gsm (0.1 psf). The most preferred areal density forfabrics/composites of this invention will range from about 50 gsm (0.01psf) to about 250 gsm (0.05 psf) prior to consolidation/molding.Articles of the invention comprising multiple fiber layers stacked oneupon another and consolidated will have a preferred composite arealdensity of from about 1000 gsm (0.2 psf) to about 40,000 gsm (8.0 psf),more preferably from about 2000 gsm (0.40 psf) to about 30,000 gsm (6.0psf), more preferably from about 3000 gsm (0.60 psf) to about 20,000 gsm(4.0 psf), and most preferably from about 3750 gsm (0.75 psf) to about15,000 gsm (3.0 psf). A typical range for composite articles shaped intohelmets is from about 7,500 gsm (1.50 psf) to about 12,500 gsm (2.50psf). Fibrous composites of the invention comprising a plurality ofadjoined fiber layers also have a preferred interlaminar lap shearstrength between fiber plies of at least about 170 pounds force (lbf),more preferably at least about 200 lbf and most preferably at leastabout 300 lbf between fiber plies, all being measured per ASTM D5868 atstandard ambient room temperature.

The fabrics of the invention may be used in various applications to forma variety of different ballistic resistant articles using well knowntechniques, including flexible, soft armor articles as well as rigid,hard armor articles. For example, suitable techniques for formingballistic resistant articles are described in, for example, U.S. Pat.Nos. 4,623,574, 4,650,710, 4,748,064, 5,552,208, 5,587,230, 6,642,159,6,841,492 and 6,846,758, all of which are incorporated herein byreference to the extent not incompatible herewith. The composites areparticularly useful for the formation of hard armor and shaped orunshaped sub-assembly intermediates formed in the process of fabricatinghard armor articles. By “hard” armor is meant an article, such ashelmets, panels for military vehicles, or protective shields, which havesufficient mechanical strength so that it maintains structural rigiditywhen subjected to a significant amount of stress and is capable of beingfreestanding without collapsing. Such hard articles are preferably, butnot exclusively, formed using a high tensile modulus binder material.

The structures can be cut into a plurality of discrete sheets andstacked for formation into an article or they can be formed into aprecursor which is subsequently used to form an article. Such techniquesare well known in the art. In a most preferred embodiment of theinvention, a plurality of fiber layers are provided, each comprising aconsolidated plurality of fiber plies, wherein a thermoplastic polymeris bonded to at least one outer surface of each fiber layer eitherbefore, during or after a consolidation step which consolidates theplurality of fiber plies, wherein the plurality of fiber layers aresubsequently merged by another consolidation step which consolidates theplurality of fiber layers into an armor article or sub-assembly of anarmor article.

The ballistic resistance properties of the fibrous composites of theinvention, including both ballistic penetration resistance and backfacesignature, may be measured according to well known techniques in theart.

The following examples serve to illustrate the invention.

EXAMPLES

The impact of fiber finish removal and optionally other fiber surfacetreatments on the flexural properties such as stress at yield andbackface signature performance of various composites was assessed,generating results as identified in Tables 2A and 2B below. The fiberprocessing techniques were conducted as follows:

Fiber Finish Removal

A plurality of multi-filament fibers was unwound from a plurality offiber spools (one spool per multi-filament fiber) and then passedthrough a fixed collimating comb to organize the fibers into an evenlyspaced fiber web. The fiber web was then directed through a pre-soakwater bath containing de-ionized water, with an approximate residencetime of about 18 seconds. After exiting the pre-soak water bath, thefibers were rinsed by a bank of 30 water nozzles. Water pressure of eachwater nozzle was approximately 42 psi with a water flow rate ofapproximately 0.5 gallons per minute per nozzle. The water exiting thenozzles was formed as a relatively flat stream and the angle of watercontact on the fibers was either 0° or 30° relative to the angle ofincidence of the stream emitting from adjacent nozzles. Watertemperature was measured as 28.9° C. Line speeds through the pre-soakwater bath and through the bank of water nozzles ranged from about 4m/min to about 20 m/min. The water in the soak bath and water deliveredto the nozzles was deionized by first passing through a separatede-ionizing system. The washed fibers were then dried and transferredfor further processing.

Table 1 summarizes representative examples provided solely to illustratehow certain washing variables affect the quantity of finish removed fromthe fiber. Each sample consisted of 4 ends bundled together on onesample spool. Each sample was run for at least 400 ft which totaled 60 gof fiber per sample. The % residue on the fiber represents agravimetrically determined measurement of the amount of finish remainingon the fiber after washing per the specified conditions in the Table.The gravimetric measurement is based on a comparison with the amount offinish present on unwashed control fibers.

TABLE 1 Nozzle Line Nozzle % Nozzle Pressure Speed Output Residue SampleStyle (psi) (Ft/min) (gpm) on Fiber I A1 42 15 0.20 2.3 II B1 30 15 0.292.4 III C1 30 15 0.41 3.1 IV C2 15 15 0.30 3.1 V A2 42 15 0.20 4.0 VI B230 15 0.29 4.1 VII A3 56 50 0.23 5.0 VIII C3 15 15 0.30 5.1 IX A4 56 300.23 5.5 X C4 30 15 0.41 5.9 XI C5 34 30 0.44 5.9 XII C6 34 60 0.44 6.2Corona Treatment

An 18-inch wide web of washed fibers was continuously passed through acorona treater having 30-inch wide electrodes at a rate of approximately15 ft/min, with the corona treater set to a power of 2 kW. This resultedin a power distribution over the area of the fibers, measured in wattdensity, of 2000 W/(2.5 Ft×15-FPM) or 53 Watts/ft²/min applied to thefibers. The residence time of the fibers within the corona field wasapproximately 2 seconds. Treatment was conducted under standardatmospheric pressure.

Plasma Treatment

A 29-inch wide web of washed fibers was continuously passed through anatmospheric plasma treater (model: Enercon Plasma3 Station ModelAPT12DF-150/2, from Enercon Industries Corp., having 29-inch wideelectrodes) at a rate of approximately 12 ft/min, with the plasmatreater set to a power of 2 kW. This resulted in a power distributionover the area of the fibers, measured in watt density, of 2000 W/(29in.×12-FPM) or 67 Watts/ft²/min applied to the fibers. The residencetime of the fibers within the plasma treater was approximately 2seconds. Treatment was conducted under standard atmospheric pressure.

Measurement of Flexural Properties

Unless specified otherwise, testing was conducted according to thespecifications of the three-point bend test method of ASTM standard D790at a standard ambient room temperature of approximately 72° F. Accordingto this process, a beam-shaped or bar-shaped specimen is placed evenlyon supports at opposite ends of the beam/bar with an open span of aspecified distance between the supports. A load is applied at aspecified rate to the center of the specimen, such as with a loadingnose, causing the specimen to bend. The load is applied for a specifiedtime. According to the method of ASTM D790, the load is applied untilthe specimen reaches 5% deflection or until the specimen breaks.

In all of the inventive examples illustrated below, flexural propertytesting was performed on non-woven fiber layers, measuring thedisplacement at yield, strain at yield, load at yield, stress at yieldand energy to yield point for a specimen having a length ofapproximately 6″ (15.24 cm), a width of approximately 0.5″ (12.7mm)±about 0.02″ (0.508 mm), a depth of approximately 0.31″ (±7.874 mm)about 0.02″ (0.508 mm) (1.5 psf areal density), with a span ofapproximately 4.8″ (12.192 cm) and a strain rate of approximately 0.01in/in/min as per ASTM D790 Procedure A. For the purposes of thisinvention, a load was applied at least until at least partialdelamination of at least a part of the composite occurs. Testing wasconducted using a universal Instron 5585 testing machine with a threepoint testing fixture.

The fibers of the tested composites were embedded in various polymericbinder (polymeric matrix) materials. Each composite comprised the samepolyethylene fiber type with each comprising a different anionic,aliphatic polyester-based polyurethane coating on the fibers. Varioustreatments are compared to show the effect of the fiber treatments wherethe fiber treatments are the only variables. The composites were formedby molding 40 2-ply fiber layers together at a temperature of about 270°F. (132° C.) and at a pressure of about 500 psi for about 10 min.

V₅₀ Measurement

V₅₀ data was acquired taken under conventionally known standardizedtechniques, particularly per the conditions of Department of DefenseTest Method Standard MIL-STD-662F.

Backface Signature Measurement

The standard method for measuring BFS of soft armor is outlined by NIJStandard 0101.04, Type IIIA, where an armor sample is place in contactwith the surface of a deformable clay backing material. This NIJ methodis conventionally used to obtain a reasonable approximation orprediction of actual BFS that may be expected during a ballistic eventin field use for armor that rests directly on or very close to the bodyof the user. However, for armor that does not rest directly on or veryclose to the body or head of the user, a better approximation orprediction of actual BFS is obtained by spacing the armor from thesurface of the deformable clay backing material. Accordingly, thebackface signature data identified in Table 2A was not measured by themethod of NIJ Standard 0101.04, Type IIIA. Instead, a method of newdesign was employed which is similar to the method of NIJ Standard0101.04, Type IIIA, but rather than laying the composite articledirectly on a flat clay block the composite was spaced apart from theclay block by ½ inch (12.7 mm) by inserting a custom machined spacerelement between the composite article and the clay block. The custommachined spacer element comprised an element having a border and aninterior cavity defined by said border wherein the clay was exposedthrough the cavity, and wherein the spacer was positioned in directcontact with front surface of the clay. Projectiles were fired at thecomposite articles at target locations corresponding to the interiorcavity of the spacer. The projectiles impacted the composite article atlocations corresponding to the interior cavity of the spacer, and eachprojectile impact caused a measurable depression in the clay. All of theBFS measurements in Table 2A refer only to the depth of the depressionin the clay as per this method and do not take into account the depth ofthe spacer element, i.e. the BFS measurements in Table 2A do not includethe actual distance between the composite and the clay.

Delamination Measurement

Delamination in Table 2A refers to the measurement of the depth of reardeformation of the actual tested panels, rather than the depth ofdepression in the backing material. Such is referred to as“delamination” because it is not the clay depression which is beingmeasured. This measurement of delamination will be less than the BFSmeasurement plus the ½″ (12.7 mm) air gap depth because after aprojectile impact, the fabric at the area of impact partially retracts.The delamination measurement is taken after said retraction, while theBFS measurement with the air gap method described herein records thefull extent of rear deformation of the fabric. Deformation after saidretraction is typically measured by cutting a cross-section of the paneland measuring the depth from the plane of the undamaged rear surface ofthe panel to the deepest outer portion of the deformed area.

For each example, BFS was measured for 12″×12″ square samples having anareal density of 2.0 lb/ft² (psf) and a fiber areal density (arealdensity of a single ply of parallel fibers, i.e. one unitape) of 53grams/m² (gsm). For each example, BFS was measured against a 9 mm,124-grain FMJ RN projectile fired at a velocity of about 1430feet/second (fps)±30 fps.

TABLE 2A BFS plus BFS plus BFS @ Delamination @ ½″ gap ½″ gap 2.0 psf2.0 psf minus minus 160° F. 160° F. Delam Delam RT (71.11° C.) RT(71.11° C.) @ RT @ 160° F. Example Product Fiber Treatment (mm) (mm)(mm) (mm) (mm) (mm) 1 I None 9.4 13.1 17.3 14.7 4.8 11.1 2 I Plasma Only6.5 9.8 13.1 12.3 6.1 10.2 Ar/O2 90/10 (2 kW) 3 I Wash & Plasma 3.4 6.311.0 11.5 5.1 7.5 Ar/O2 90/10 (3 kW) 4 II None 8.3 11.3 16.3 17.0 4.77.0 5 II Washed 10.5 11.5 14.5 18.4 8.7 5.8 6 II Plasma Only 5.3 7.513.3 14.1 4.7 6.1 Ar/O2 90/10 (2 kW) 7 II Wash & Plasma 1.9 4.7 12.311.9 2.3 5.5 Ar/O2 90/10 (3 kW) 8 II Wash & Plasma 2.3 4.1 12.1 15.5 2.81.3 Ar/O2 90/10 (1.5 kW) 9 III None 12.4 14.9 15.6 14.9 9.5 12.7 10 IIIWashed 11.5 10.3 11.8 14.3 12.4 8.7 11 III Plasma Only 6.9 11.7 9.8 10.19.8 14.3 Ar/O2 90/10 (2 kW) 12 III Wash & Plasma 5.1 6.1 12.8 12.1 5.16.7 Ar/O2 90/10 (3 kW) 13 IV None 5.3 14.3 12.5 14.8 5.5 12.2 14 IV Wash& Plasma 6.3 9.6 14.3 13.8 4.7 8.6 Ar/O2 90/10 (3 kW) 15 V Wash & Plasma3.8 6.1 14.9 13.7 1.6 5.1 Ar/O2 90/10 (3 kW) 16 VI Wash & Plasma 3.1 6.412.8 13.6 3.1 5.5 Ar/O2 90/10 (3 kW)

Table 2A illustrates the differences in measured BFS and delaminationwhen comparing fabrics formed from unwashed and untreated fibersrelative to fabrics formed from fibers that were subjected to varioustreatments. Each of products I-VI comprised the same polyethylene fibertype with each comprising a different anionic, aliphatic polyester-basedpolyurethane coating on the fibers. The last two columns in Table 2Aidentifying BFS plus ½″ (12.7 mm) gap minus delamination identify theamount of fabric retraction and illustrate the greater accuracy of theair gap spacer BFS measurement method for measuring the full expectedextent of BFS of hard armor in actual field use.

TABLE 2B Three Point Bend V₅₀ ASTM D790 17 grain Stress at Energy toExam- @ 1.0 psf Yield Yield ple Product Fiber Treatment (fps) (ksi)(Lbf-in) 1 I None 1848 4.40 1.14 2 I Plasma Only 1810 6.22 6.89 Ar/O290/10 (2 kW) 3 I Wash & Plasma 1894 9.80 32.31 Ar/O2 90/10 (3 kW) 4 IINone 1798 — — 5 II Washed 1899 — — 6 II Plasma Only 1771 — — Ar/O2 90/10(2 kW) 7 II Wash & Plasma 1752 11.39 25.43 Ar/O2 90/10 (3 kW) 8 II Wash& Plasma 1767 11.36 22.97 Ar/O2 90/10 (1.5 kW) 9 III None 1902 — — 10III Washed 1889 — — 11 III Plasma Only 1828 — — Ar/O2 90/10 (2 kW) 12III Wash & Plasma 1897 9.13 31.55 Ar/O2 90/10 (3 kW) 13 IV None 18134.28 3.02 14 IV Wash & Plasma 1814 6.33 9.77 Ar/O2 90/10 (3 kW) 15 VWash & Plasma 1917 11.04 41.04 Ar/O2 90/10 (3 kW) 16 VI Wash & Plasma1850 10.98 49.56 Ar/O2 90/10 (3 kW)

Table 2B illustrates differences in ballistic penetration resistance(V₅₀) and three point bend properties as distinguished by fibertreatment.

While the present invention has been particularly shown and describedwith reference to preferred embodiments, it will be readily appreciatedby those of ordinary skill in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention. It is intended that the claims be interpreted to coverthe disclosed embodiment, those alternatives which have been discussedabove and all equivalents thereto.

What is claimed is:
 1. A method of forming a fibrous compositecomprising at least two adjoined fiber layers, each fiber layercomprising fibers having surfaces that are at least partially coveredwith a polymeric material, and wherein less than 50% of the fibersurface area is covered by a fiber surface finish, which fiber surfacefinish is between the fiber surface and said polymeric material; saidcomposite having a stress at yield of at least 7.50 ksi (˜51.71 MPa) asmeasured by ASTM D790 for a composite having an areal density of about1.5 lb/ft² (7.32 kg/m²) or less, the method comprising providing aplurality of polymeric fibers wherein less than 50% of the fiber surfacearea of said fibers is covered by a fiber surface finish; optionallytreating the fiber surfaces to enhance the surface adsorbability,bonding or adhesion of a subsequently applied polymeric material to thefiber surfaces; applying a polymeric material onto at least a portion ofsaid fibers, thereby adsorbing, bonding or adhering the polymericmaterial on or to the fiber surfaces; producing a plurality of fiberlayers from said fibers either before or after applying said polymericmaterial to said fibers; and consolidating said plurality of fiberlayers to produce a fibrous composite.
 2. The method of claim 1 whereinsaid optional step of treating the fiber surfaces to enhance the surfaceadsorbability, bonding or adhesion of a subsequently applied polymericmaterial to the fiber surfaces is conducted.
 3. The method of claim 1wherein said fiber treatment comprises a plasma treatment or a coronatreatment.
 4. The method of claim 1 wherein a pre-existing fiber surfacefinish is removed by washing the fibers with water.
 5. The method ofclaim 1 wherein at least one of said fiber layers is formed by weaving aplurality of said fibers into a woven fabric.
 6. The method of claim 1wherein at least one of said fiber layers is formed by arranging aplurality of said fibers into a non-woven fabric.
 7. The method of claim1 wherein patches of residual finish are present on the fiber surfacesof each fiber between the fiber surface and the polymeric material,wherein from 90% to 99.0% of the fiber surface area is not covered bythe residual fiber surface finish.
 8. The method of claim 1 wherein thecomposite formed by the method has a backface signature of less thanabout 8 mm when impacted with a 124-grain, 9 mm FMJ RN projectile firedat a velocity of from about 427 m/s to about 445 m/s (1430 feet/second(fps)±30 fps), wherein backface signature is measured for a compositehaving an areal density of 2.0 psf.
 9. The method of claim 1 wherein thecomposite formed by the method has a V₅₀ value of at least about 1750feet/sec (fps) (533.40 m/s) against a 9 mm projectile in accordance withDepartment of Defense Test Method Standard MIL-STD-662F.
 10. A method offorming a fibrous composite comprising at least two adjoined fiberlayers, each fiber layer comprising fibers having surfaces that are atleast partially covered with a polymeric material, and wherein less than50% of the fiber surface area is covered by a fiber surface finish; themethod comprising providing a plurality of polymeric fibers wherein lessthan 50% of the fiber surface area of said fibers is covered by a fibersurface finish; optionally treating the fiber surfaces to enhance thesurface adsorbability, bonding or adhesion of a subsequently appliedpolymeric material to the fiber surfaces; applying a polymeric materialonto at least a portion of said fibers, thereby adsorbing, bonding oradhering the polymeric material on or to the fiber surfaces; producing aplurality of fiber layers from said fibers either before or afterapplying said polymeric material to said fibers; and consolidating saidplurality of fiber layers to produce a fibrous composite; said fibrouscomposite having a stress at yield that is greater than the stress atyield of a comparable fibrous composite having a fiber surface finish ongreater than 50% of the surface area of their fibers wherein such afiber surface finish is between the fiber surfaces and the polymericmaterial.
 11. The method of claim 10 wherein said optional step oftreating the fiber surfaces to enhance the bonding and/or adhesion of asubsequently applied material to the fiber surfaces is conducted. 12.The method of claim 11 wherein said fiber treatment comprises a plasmatreatment or a corona treatment.
 13. The method of claim 10 wherein saidcomposite comprises polyethylene fibers having a tenacity of 20 g/denieror more.
 14. The method of claim 10 wherein at least one of said fiberlayers is formed by weaving a plurality of said fibers into a wovenfabric.
 15. The method of claim 10 wherein at least one of said fiberlayers is formed by arranging a plurality of said fibers into anon-woven fabric.
 16. The method of claim 10 wherein a pre-existingfiber surface finish is partially removed from the fibers.
 17. Themethod of claim 16 wherein patches of residual finish are present on thefiber surfaces between the fiber surface and the polymeric material,wherein from 90% to 99.0% of the fiber surface area is not covered bythe residual fiber surface finish, and wherein each fiber layer of thecomposite is impregnated with a thermoplastic polymeric binder.
 18. Themethod of claim 16 wherein said pre-existing fiber surface finish isremoved by washing the fibers with water.
 19. The method of claim 10wherein said fibers have a tenacity of 20 g/denier or more.